# Stream

#### abstract class Stream[+A] extends LinearSeq[A] with GenericTraversableTemplate[A, Stream] with LinearSeqOptimized[A, Stream[A]]

The class `Stream` implements lazy lists where elements are only evaluated when they are needed. Here is an example:

``` import scala.math.BigInt
object Main extends App {

val fibs: Stream[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip(fibs.tail).map { n => n._1 + n._2 }

fibs take 5 foreach println
}

// prints
//
// 0
// 1
// 1
// 2
// 3
```

The `Stream` class also employs memoization such that previously computed values are converted from `Stream` elements to concrete values of type `A`. To illustrate, we will alter body of the `fibs` value above and take some more values:

``` import scala.math.BigInt
object Main extends App {

val fibs: Stream[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip(
fibs.tail).map(n => {
n._1 + n._2
})

fibs take 5 foreach println
fibs take 6 foreach println
}

// prints
//
// 0
// 1
// 1
// 2
// 3

// And then prints
//
// 0
// 1
// 1
// 2
// 3
// 5
```

There are a number of subtle points to the above example.

• The definition of `fibs` is a `val` not a method. The memoization of the `Stream` requires us to have somewhere to store the information and a `val` allows us to do that.
• While the `Stream` is actually being modified during access, this does not change the notion of its immutability. Once the values are memoized they do not change and values that have yet to be memoized still "exist", they simply haven't been realized yet.
• One must be cautious of memoization; you can very quickly eat up large amounts of memory if you're not careful. The reason for this is that the memoization of the `Stream` creates a structure much like List. So long as something is holding on to the head, the head holds on to the tail, and so it continues recursively. If, on the other hand, there is nothing holding on to the head (e.g. we used `def` to define the `Stream`) then once it is no longer being used directly, it disappears.
``` // For example, let's build the natural numbers and do some silly iteration
// over them.

def loop(s: String, i: Int, iter: Iterator[Int]): Unit = {
// Stop after 200,000
if (i < 200001) {
if (i % 50000 == 0) println(s + i)
loop(s, iter.next, iter)
}
}

// Our first Stream definition will be a val definition
val stream1: Stream[Int] = {
def loop(v: Int): Stream[Int] = v #:: loop(v + 1)
loop(0)
}

// Because stream1 is a val, everything that the iterator produces is held
// by virtue of the fact that the head of the Stream is held in stream1
val it1 = stream1.iterator
loop("Iterator1: ", it1.next, it1)

// We can redefine this Stream such that all we have is the Iterator left
// and allow the Stream to be garbage collected as required.  Using a def
// to provide the Stream ensures that no val is holding onto the head as
// is the case with stream1
def stream2: Stream[Int] = {
def loop(v: Int): Stream[Int] = v #:: loop(v + 1)
loop(0)
}
val it2 = stream2.iterator
loop("Iterator2: ", it2.next, it2)

// And, of course, we don't actually need a Stream at all for such a simple
// problem.  There's no reason to use a Stream if you don't actually need
// one.
val it3 = new Iterator[Int] {
var i = -1
def hasNext = true
def next: Int = { i += 1; i }
}
loop("Iterator3: ", it3.next, it3)
```
• The fact that `tail` works at all is of interest. In the definition of `fibs` we have an initial `(0, 1, Stream(...))` so `tail` is deterministic. If we deinfed `fibs` such that only `0` were concretely known then the act of determining `tail` would require the evaluation of `tail` which would cause an infinite recursion and stack overflow. If we define a definition where the tail is not initially computable then we're going to have an infinite recursion:
``` // The first time we try to access the tail we're going to need more
// information which will require us to recurse, which will require us to
// recurse, which...
val sov: Stream[Vector[Int]] = Vector(0) #:: sov.zip(sov.tail).map { n => n._1 ++ n._2 }
```

The definition of `fibs` above creates a larger number of objects than necessary depending on how you might want to implement it. The following implementation provides a more "cost effective" implementation due to the fact that it has a more direct route to the numbers themselves:

``` lazy val fib: Stream[Int] = {
def loop(h: Int, n: Int): Stream[Int] = h #:: loop(n, h + n)
loop(1, 1)
}
```
A

the type of the elements contained in this stream.

Self Type
Stream[A]
Source
Stream.scala
Version

1.1 08/08/03

Since

2.8

"Scala's Collection Library overview" section on `Streams` for more information.

Linear Supertypes
Known Subclasses
Ordering
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Inherited
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1. Stream
2. LinearSeqOptimized
3. LinearSeq
4. LinearSeq
5. LinearSeqLike
6. Seq
7. Seq
8. SeqLike
9. GenSeq
10. GenSeqLike
11. PartialFunction
12. Function1
13. Iterable
14. Iterable
15. IterableLike
16. Equals
17. GenIterable
18. GenIterableLike
19. Traversable
20. Immutable
21. Traversable
22. GenTraversable
23. GenericTraversableTemplate
24. TraversableLike
25. GenTraversableLike
26. Parallelizable
27. TraversableOnce
28. GenTraversableOnce
30. HasNewBuilder
31. AnyRef
32. Any
Visibility
1. Public
2. All

### Type Members

1. #### type Self = Stream[A]

The type implementing this traversable

The type implementing this traversable

Attributes
protected
Definition Classes
TraversableLike
2. #### final class StreamWithFilter extends WithFilter

A lazier implementation of WithFilter than TraversableLike's.

3. #### class WithFilter extends FilterMonadic[A, Repr]

A class supporting filtered operations.

### Abstract Value Members

1. #### abstract def tailDefined: Boolean

Is the tail of this stream defined?

Is the tail of this stream defined?

Attributes
protected

### Concrete Value Members

1. #### final def !=(arg0: AnyRef): Boolean

Definition Classes
AnyRef
2. #### final def !=(arg0: Any): Boolean

Test two objects for inequality.

Test two objects for inequality.

returns

`true` if !(this == that), false otherwise.

Definition Classes
Any
3. #### final def ##(): Int

Equivalent to `x.hashCode` except for boxed numeric types.

Equivalent to `x.hashCode` except for boxed numeric types. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them.

returns

a hash value consistent with ==

Definition Classes
AnyRef → Any
4. #### def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Create a new stream which contains all elements of this stream followed by all elements of Traversable `that`.

Create a new stream which contains all elements of this stream followed by all elements of Traversable `that`.

B

The element type of the returned collection.That

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

that

The GenTraversableOnce the be contatenated to this `Stream`.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

A new collection containing the result of concatenating `this` with `that`.

Definition Classes
StreamTraversableLikeGenTraversableLike
Note

This method doesn't cause the `Stream` to be fully realized but it should be noted that using the `++` operator from another collection type could cause infinite realization of a `Stream`. For example, referring to the definition of `fibs` in the preamble, the following would never return: `List(BigInt(12)) ++ fibs`.

,

It's subtle why this works. We know that if the target type of the Builder `That` is either a `Stream`, or one of its supertypes, or undefined, then `StreamBuilder` will be chosen for the implicit. We recognize that fact and optimize to get more laziness.

5. #### def ++:[B >: A, That](that: Traversable[B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That

As with `++`, returns a new collection containing the elements from the left operand followed by the elements from the right operand.

As with `++`, returns a new collection containing the elements from the left operand followed by the elements from the right operand. It differs from `++` in that the right operand determines the type of the resulting collection rather than the left one.

Example:

```    scala> val x = List(1)
x: List[Int] = List(1)

scala> val z = x ++: y
```

This overload exists because: for the implementation of `++:` we should reuse that of `++` because many collections override it with more efficient versions.

Since `TraversableOnce` has no `++` method, we have to implement that directly, but `Traversable` and down can use the overload.

B

the element type of the returned collection.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

that

the traversable to append.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new stream which contains all elements of this stream followed by all elements of `that`.

Definition Classes
TraversableLike
6. #### abstract def ++:[B](that: TraversableOnce[B]): Stream[B]

[use case] Concatenates this stream with the elements of a traversable collection.

[use case]

Concatenates this stream with the elements of a traversable collection. It differs from ++ in that the right operand determines the type of the resulting collection rather than the left one.

B

the element type of the returned collection.

that

the traversable to append.

returns

a new collection of type `That` which contains all elements of this stream followed by all elements of `that`.

Definition Classes
TraversableLike
7. #### def ++:[B >: A, That](that: TraversableOnce[B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Concatenates this stream with the elements of a traversable collection.

Concatenates this stream with the elements of a traversable collection. It differs from ++ in that the right operand determines the type of the resulting collection rather than the left one.

Example:

```    scala> val x = List(1)
x: List[Int] = List(1)

scala> val z = x ++: y
```
B

the element type of the returned collection.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

that

the traversable to append.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new collection of type `That` which contains all elements of this stream followed by all elements of `that`.

Definition Classes
TraversableLike
8. #### abstract def +:(elem: A): Stream[A]

[use case] A copy of the stream with an element prepended.

[use case]

A copy of the stream with an element prepended.

elem

the prepended element

returns

a new collection of type `That` consisting of `elem` followed by all elements of this stream.

Definition Classes
GenSeqLike
9. #### def +:[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

A copy of the stream with an element prepended.

A copy of the stream with an element prepended.

Note that :-ending operators are right associative (see example). Also, the original stream is not modified, so you will want to capture the result.

Example:

```     scala> val x = LinkedList(1)

scala> val y = 2 +: x

scala> println(x)
```
B

the element type of the returned stream.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

elem

the prepended element

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new collection of type `That` consisting of `elem` followed by all elements of this stream.

Definition Classes
StreamSeqLikeGenSeqLike
10. #### def /:[B](z: B)(op: (B, A) ⇒ B): B

Applies a binary operator to a start value and all elements of this stream, going left to right.

Applies a binary operator to a start value and all elements of this stream, going left to right.

Note: `/:` is alternate syntax for `foldLeft`; `z /: xs` is the same as `xs foldLeft z`.

Examples:

Note that the folding function used to compute b is equivalent to that used to compute c.

```     scala> val a = LinkedList(1,2,3,4)

scala> val b = (5 /: a)(_+_)
b: Int = 15

scala> val c = (5 /: a)((x,y) => x + y)
c: Int = 15
```

Note: will not terminate for infinite-sized collections.

B

the result type of the binary operator.

z

the start value.

op

the binary operator.

returns

the result of inserting `op` between consecutive elements of this stream, going left to right with the start value `z` on the left:

```            op(...op(op(z, x1), x2), ..., xn)
```

where `x1, ..., xn` are the elements of this stream.

Definition Classes
TraversableOnceGenTraversableOnce
11. #### def /:\[A1 >: A](z: A1)(op: (A1, A1) ⇒ A1): A1

A syntactic sugar for out of order folding.

A syntactic sugar for out of order folding. See `fold`.

Example:

```     scala> val a = LinkedList(1,2,3,4)

scala> val b = (a /:\ 5)(_+_)
b: Int = 15
```
Definition Classes
GenTraversableOnce
12. #### abstract def :+(elem: A): Stream[A]

[use case] A copy of this stream with an element appended.

[use case]

A copy of this stream with an element appended.

elem

the appended element

returns

a new collection of type `That` consisting of all elements of this stream followed by `elem`.

Definition Classes
GenSeqLike
13. #### def :+[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

A copy of this stream with an element appended.

A copy of this stream with an element appended.

Note: will not terminate for infinite-sized collections.

B

the element type of the returned stream.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

elem

the appended element

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new collection of type `That` consisting of all elements of this stream followed by `elem`.

Definition Classes
SeqLikeGenSeqLike
14. #### def :\[B](z: B)(op: (A, B) ⇒ B): B

Applies a binary operator to all elements of this stream and a start value, going right to left.

Applies a binary operator to all elements of this stream and a start value, going right to left.

Note: `:\` is alternate syntax for `foldRight`; `xs :\ z` is the same as `xs foldRight z`.

Note: will not terminate for infinite-sized collections.

Examples:

Note that the folding function used to compute b is equivalent to that used to compute c.

```     scala> val a = LinkedList(1,2,3,4)

scala> val b = (a :\ 5)(_+_)
b: Int = 15

scala> val c = (a :\ 5)((x,y) => x + y)
c: Int = 15

```
B

the result type of the binary operator.

z

the start value

op

the binary operator

returns

the result of inserting `op` between consecutive elements of this stream, going right to left with the start value `z` on the right:

```            op(x1, op(x2, ... op(xn, z)...))
```

where `x1, ..., xn` are the elements of this stream.

Definition Classes
TraversableOnceGenTraversableOnce
15. #### final def ==(arg0: AnyRef): Boolean

Definition Classes
AnyRef
16. #### final def ==(arg0: Any): Boolean

Test two objects for equality.

Test two objects for equality.

returns

`true` if the receiver object is equivalent to the argument; `false` otherwise.

Definition Classes
Any
17. #### def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder

Write all defined elements of this iterable into given string builder.

Write all defined elements of this iterable into given string builder. The written text begins with the string `start` and is finished by the string `end`. Inside, the string representations of defined elements (w.r.t. the method `toString()`) are separated by the string `sep`. The method will not force evaluation of undefined elements. A tail of such elements will be represented by a `"?"` instead.

b

The collection.mutable.StringBuilder factory to which we need to add the string elements.

start

The prefix of the resulting string (e.g. "Stream(")

sep

The separator between elements of the resulting string (e.g. ",")

end

The end of the resulting string (e.g. ")")

returns

The original collection.mutable.StringBuilder containing the resulting string.

Definition Classes
StreamTraversableOnce
18. #### def addString(b: StringBuilder): StringBuilder

Appends all elements of this stream to a string builder.

Appends all elements of this stream to a string builder. The written text consists of the string representations (w.r.t. the method `toString`) of all elements of this stream without any separator string.

Example:

```     scala> val a = LinkedList(1,2,3,4)

scala> val b = new StringBuilder()
b: StringBuilder =

b: StringBuilder = 1234
```
b

the string builder to which elements are appended.

returns

the string builder `b` to which elements were appended.

Definition Classes
TraversableOnce
19. #### def addString(b: StringBuilder, sep: String): StringBuilder

Appends all elements of this stream to a string builder using a separator string.

Appends all elements of this stream to a string builder using a separator string. The written text consists of the string representations (w.r.t. the method `toString`) of all elements of this stream, separated by the string `sep`.

Example:

```     scala> val a = LinkedList(1,2,3,4)

scala> val b = new StringBuilder()
b: StringBuilder =

res0: StringBuilder = 1, 2, 3, 4
```
b

the string builder to which elements are appended.

sep

the separator string.

returns

the string builder `b` to which elements were appended.

Definition Classes
TraversableOnce
20. #### def aggregate[B](z: B)(seqop: (B, A) ⇒ B, combop: (B, B) ⇒ B): B

Aggregates the results of applying an operator to subsequent elements.

Aggregates the results of applying an operator to subsequent elements.

This is a more general form of `fold` and `reduce`. It has similar semantics, but does not require the result to be a supertype of the element type. It traverses the elements in different partitions sequentially, using `seqop` to update the result, and then applies `combop` to results from different partitions. The implementation of this operation may operate on an arbitrary number of collection partitions, so `combop` may be invoked an arbitrary number of times.

For example, one might want to process some elements and then produce a `Set`. In this case, `seqop` would process an element and append it to the list, while `combop` would concatenate two lists from different partitions together. The initial value `z` would be an empty set.

```   pc.aggregate(Set[Int]())(_ += process(_), _ ++ _)
```

Another example is calculating geometric mean from a collection of doubles (one would typically require big doubles for this).

B

the type of accumulated results

z

the initial value for the accumulated result of the partition - this will typically be the neutral element for the `seqop` operator (e.g. `Nil` for list concatenation or `0` for summation)

seqop

an operator used to accumulate results within a partition

combop

an associative operator used to combine results from different partitions

Definition Classes
TraversableOnceGenTraversableOnce
21. #### def andThen[C](k: (A) ⇒ C): PartialFunction[Int, C]

Composes this partial function with a transformation function that gets applied to results of this partial function.

Composes this partial function with a transformation function that gets applied to results of this partial function.

C

the result type of the transformation function.

k

the transformation function

returns

a partial function with the same domain as this partial function, which maps arguments `x` to `k(this(x))`.

Definition Classes
PartialFunctionFunction1
22. #### def append[B >: A](rest: ⇒ TraversableOnce[B]): Stream[B]

The stream resulting from the concatenation of this stream with the argument stream.

The stream resulting from the concatenation of this stream with the argument stream.

rest

The stream that gets appended to this stream

returns

The stream containing elements of this stream and the traversable object.

23. #### def apply(n: Int): A

Selects an element by its index in the stream.

Selects an element by its index in the stream. Note: the execution of `apply` may take time proportial to the index value.

returns

the element of this stream at index `idx`, where `0` indicates the first element.

Definition Classes
LinearSeqOptimizedSeqLikeGenSeqLike
Exceptions thrown
`IndexOutOfBoundsException`

if `idx` does not satisfy `0 <= idx < length`.

24. #### final def asInstanceOf[T0]: T0

Cast the receiver object to be of type `T0`.

Cast the receiver object to be of type `T0`.

Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression `1.asInstanceOf[String]` will throw a `ClassCastException` at runtime, while the expression `List(1).asInstanceOf[List[String]]` will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

returns

Definition Classes
Any
Exceptions thrown
ClassCastException

if the receiver object is not an instance of the erasure of type `T0`.

25. #### def canEqual(that: Any): Boolean

Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.

Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.

that

The object with which this stream should be compared

returns

`true`, if this stream can possibly equal `that`, `false` otherwise. The test takes into consideration only the run-time types of objects but ignores their elements.

Definition Classes
IterableLikeEquals
26. #### def clone(): AnyRef

Create a copy of the receiver object.

Create a copy of the receiver object.

The default implementation of the `clone` method is platform dependent.

returns

a copy of the receiver object.

Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
()
Note

not specified by SLS as a member of AnyRef

27. #### abstract def collect[B](pf: PartialFunction[A, B]): Stream[B]

[use case] Builds a new collection by applying a partial function to all elements of this stream on which the function is defined.

[use case]

Builds a new collection by applying a partial function to all elements of this stream on which the function is defined.

B

the element type of the returned collection.

pf

the partial function which filters and maps the stream.

returns

a new collection of type `That` resulting from applying the partial function `pf` to each element on which it is defined and collecting the results. The order of the elements is preserved.

Definition Classes
GenTraversableLike
28. #### final def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Builds a new collection by applying a partial function to all elements of this stream on which the function is defined.

Builds a new collection by applying a partial function to all elements of this stream on which the function is defined.

B

the element type of the returned collection.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

pf

the partial function which filters and maps the stream.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new collection of type `That` resulting from applying the partial function `pf` to each element on which it is defined and collecting the results. The order of the elements is preserved.

Definition Classes
StreamTraversableLikeGenTraversableLike
29. #### def collectFirst[B](pf: PartialFunction[A, B]): Option[B]

Finds the first element of the stream for which the given partial function is defined, and applies the partial function to it.

Finds the first element of the stream for which the given partial function is defined, and applies the partial function to it.

Note: may not terminate for infinite-sized collections.

pf

the partial function

returns

an option value containing pf applied to the first value for which it is defined, or `None` if none exists.

Definition Classes
TraversableOnce
Example:
1. `Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)`

30. #### def combinations(n: Int): Iterator[Stream[A]]

Iterates over combinations.

Iterates over combinations.

returns

An Iterator which traverses the possible n-element combinations of this stream.

Definition Classes
SeqLike
Example:
1. `"abbbc".combinations(2) = Iterator(ab, ac, bb, bc)`

31. #### def companion: GenericCompanion[Stream]

The factory companion object that builds instances of class Stream.

The factory companion object that builds instances of class Stream. (or its `Iterable` superclass where class Stream is not a `Seq`.)

Definition Classes
StreamLinearSeqLinearSeqSeqSeqGenSeqIterableIterableGenIterableTraversableTraversableGenTraversableGenericTraversableTemplate
32. #### def compose[A](g: (A) ⇒ Int): (A) ⇒ A

Composes two instances of Function1 in a new Function1, with this function applied last.

Composes two instances of Function1 in a new Function1, with this function applied last.

A

the type to which function `g` can be applied

g

a function A => T1

returns

a new function `f` such that `f(x) == apply(g(x))`

Definition Classes
Function1
33. #### def contains(elem: Any): Boolean

Tests whether this stream contains a given value as an element.

Tests whether this stream contains a given value as an element.

Note: may not terminate for infinite-sized collections.

elem

the element to test.

returns

`true` if this stream has an element that is is equal (wrt `==`) to `elem`, `false` otherwise.

Definition Classes
SeqLike
34. #### def containsSlice[B](that: GenSeq[B]): Boolean

Tests whether this stream contains a given sequence as a slice.

Tests whether this stream contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

that

the sequence to test

returns

`true` if this stream contains a slice with the same elements as `that`, otherwise `false`.

Definition Classes
SeqLike
35. #### abstract def copyToArray(xs: Array[A], start: Int, len: Int): Unit

[use case] Copies elements of this stream to an array.

[use case]

Copies elements of this stream to an array. Fills the given array `xs` with at most `len` elements of this stream, starting at position `start`. Copying will stop once either the end of the current stream is reached, or the end of the array is reached, or `len` elements have been copied.

xs

the array to fill.

start

the starting index.

len

the maximal number of elements to copy.

Definition Classes
TraversableLike
36. #### def copyToArray[B >: A](xs: Array[B], start: Int, len: Int): Unit

Copies elements of this stream to an array.

Copies elements of this stream to an array. Fills the given array `xs` with at most `len` elements of this stream, starting at position `start`. Copying will stop once either the end of the current stream is reached, or the end of the array is reached, or `len` elements have been copied.

Note: will not terminate for infinite-sized collections.

B

the type of the elements of the array.

xs

the array to fill.

start

the starting index.

len

the maximal number of elements to copy.

Definition Classes
IterableLikeTraversableLikeTraversableOnceGenTraversableOnce
37. #### abstract def copyToArray(xs: Array[A]): Unit

[use case] Copies values of this stream to an array.

[use case]

Copies values of this stream to an array. Fills the given array `xs` with values of this stream. Copying will stop once either the end of the current stream is reached, or the end of the array is reached.

xs

the array to fill.

Definition Classes
GenTraversableOnce
38. #### def copyToArray[B >: A](xs: Array[B]): Unit

Copies values of this stream to an array.

Copies values of this stream to an array. Fills the given array `xs` with values of this stream. Copying will stop once either the end of the current stream is reached, or the end of the array is reached.

Note: will not terminate for infinite-sized collections.

B

the type of the elements of the array.

xs

the array to fill.

Definition Classes
TraversableOnceGenTraversableOnce
39. #### abstract def copyToArray(xs: Array[A], start: Int): Unit

[use case] Copies values of this stream to an array.

[use case]

Copies values of this stream to an array. Fills the given array `xs` with values of this stream, beginning at index `start`. Copying will stop once either the end of the current stream is reached, or the end of the array is reached.

xs

the array to fill.

start

the starting index.

Definition Classes
GenTraversableOnce
40. #### def copyToArray[B >: A](xs: Array[B], start: Int): Unit

Copies values of this stream to an array.

Copies values of this stream to an array. Fills the given array `xs` with values of this stream, beginning at index `start`. Copying will stop once either the end of the current stream is reached, or the end of the array is reached.

Note: will not terminate for infinite-sized collections.

B

the type of the elements of the array.

xs

the array to fill.

start

the starting index.

Definition Classes
TraversableOnceGenTraversableOnce
41. #### def copyToBuffer[B >: A](dest: Buffer[B]): Unit

Copies all elements of this stream to a buffer.

Copies all elements of this stream to a buffer.

Note: will not terminate for infinite-sized collections.

dest

The buffer to which elements are copied.

Definition Classes
TraversableOnce
42. #### def corresponds[B](that: GenSeq[B])(p: (A, B) ⇒ Boolean): Boolean

Tests whether every element of this stream relates to the corresponding element of another sequence by satisfying a test predicate.

Tests whether every element of this stream relates to the corresponding element of another sequence by satisfying a test predicate.

B

the type of the elements of `that`

that

the other sequence

p

the test predicate, which relates elements from both sequences

returns

`true` if both sequences have the same length and `p(x, y)` is `true` for all corresponding elements `x` of this stream and `y` of `that`, otherwise `false`.

Definition Classes
SeqLikeGenSeqLike
43. #### def count(p: (A) ⇒ Boolean): Int

Counts the number of elements in the stream which satisfy a predicate.

Counts the number of elements in the stream which satisfy a predicate.

p

the predicate used to test elements.

returns

the number of elements satisfying the predicate `p`.

Definition Classes
LinearSeqOptimizedTraversableOnceGenTraversableOnce
44. #### abstract def diff(that: Seq[A]): Stream[A]

[use case] Computes the multiset difference between this stream and another sequence.

[use case]

Computes the multiset difference between this stream and another sequence.

Note: will not terminate for infinite-sized collections.

that

the sequence of elements to remove

returns

a new collection of type `That` which contains all elements of this stream except some of occurrences of elements that also appear in `that`. If an element value `x` appears n times in `that`, then the first n occurrences of `x` will not form part of the result, but any following occurrences will.

Definition Classes
SeqLike
45. #### def diff[B >: A](that: GenSeq[B]): Stream[A]

Computes the multiset difference between this stream and another sequence.

Computes the multiset difference between this stream and another sequence.

Note: will not terminate for infinite-sized collections.

B

the element type of the returned stream.

that

the sequence of elements to remove

returns

a new collection of type `That` which contains all elements of this stream except some of occurrences of elements that also appear in `that`. If an element value `x` appears n times in `that`, then the first n occurrences of `x` will not form part of the result, but any following occurrences will.

Definition Classes
SeqLikeGenSeqLike
46. #### def distinct: Stream[A]

Builds a new stream from this stream in which any duplicates (wrt to ==) have been removed.

Builds a new stream from this stream in which any duplicates (wrt to ==) have been removed. Among duplicate elements, only the first one is retained in the resulting `Stream`.

returns

A new `Stream` representing the result of applying distinctness to the original `Stream`.

Definition Classes
StreamSeqLikeGenSeqLike
Example:
1. ```// Creates a Stream where every element is duplicated
def naturalsFrom(i: Int): Stream[Int] = i #:: { i #:: naturalsFrom(i + 1) }
naturalsFrom(1) take 6 mkString ", "
// produces: "1, 1, 2, 2, 3, 3"
(naturalsFrom(1) distinct) take 6 mkString ", "
// produces: "1, 2, 3, 4, 5, 6"
```
47. #### final def drop(n: Int): Stream[A]

Selects all elements except first n ones.

Selects all elements except first n ones.

n

the number of elements to drop from this stream.

returns

a stream consisting of all elements of this stream except the first `n` ones, or else the empty stream, if this stream has less than `n` elements.

Definition Classes
StreamLinearSeqOptimizedIterableLikeTraversableLikeGenTraversableLike
Annotations
()
48. #### def dropRight(n: Int): Stream[A]

Selects all elements except last n ones.

Selects all elements except last n ones.

n

The number of elements to take

returns

a stream consisting of all elements of this stream except the last `n` ones, or else the empty stream, if this stream has less than `n` elements.

Definition Classes
LinearSeqOptimizedIterableLike
49. #### def dropWhile(p: (A) ⇒ Boolean): Stream[A]

Returns the a `Stream` representing the longest suffix of this iterable whose first element does not satisfy the predicate `p`.

Returns the a `Stream` representing the longest suffix of this iterable whose first element does not satisfy the predicate `p`.

p

the test predicate.

returns

A new `Stream` representing the results of applying `p` to the oringal `Stream`.

Definition Classes
StreamTraversableLikeGenTraversableLike
Example:
1. ```// Assume we have a Stream that takes the first 20 natural numbers
def naturalsLt50(i: Int): Stream[Int] = i #:: { if (i < 20) naturalsLt50(i * + 1) else Stream.Empty }
naturalsLt50(0) dropWhile { _ < 10 }
// produces: "10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20"
```
Note

This method realizes the entire `Stream` beyond the truth value of the predicate `p`.

50. #### def endsWith[B](that: GenSeq[B]): Boolean

Tests whether this stream ends with the given sequence.

Tests whether this stream ends with the given sequence.

Note: will not terminate for infinite-sized collections.

that

the sequence to test

returns

`true` if this stream has `that` as a suffix, `false` otherwise.

Definition Classes
SeqLikeGenSeqLike
51. #### final def eq(arg0: AnyRef): Boolean

Tests whether the argument (`arg0`) is a reference to the receiver object (`this`).

Tests whether the argument (`arg0`) is a reference to the receiver object (`this`).

The `eq` method implements an equivalence relation on non-null instances of `AnyRef`, and has three additional properties:

• It is consistent: for any non-null instances `x` and `y` of type `AnyRef`, multiple invocations of `x.eq(y)` consistently returns `true` or consistently returns `false`.
• For any non-null instance `x` of type `AnyRef`, `x.eq(null)` and `null.eq(x)` returns `false`.
• `null.eq(null)` returns `true`.

When overriding the `equals` or `hashCode` methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (`o1 eq o2`), they should be equal to each other (`o1 == o2`) and they should hash to the same value (`o1.hashCode == o2.hashCode`).

returns

`true` if the argument is a reference to the receiver object; `false` otherwise.

Definition Classes
AnyRef
52. #### def equals(that: Any): Boolean

The equals method for arbitrary sequences.

The equals method for arbitrary sequences. Compares this sequence to some other object.

that

The object to compare the sequence to

returns

`true` if `that` is a sequence that has the same elements as this sequence in the same order, `false` otherwise

Definition Classes
GenSeqLikeEquals → AnyRef → Any
53. #### def exists(p: (A) ⇒ Boolean): Boolean

Tests whether a predicate holds for some of the elements of this stream.

Tests whether a predicate holds for some of the elements of this stream.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

`true` if the given predicate `p` holds for some of the elements of this stream, otherwise `false`.

Definition Classes
LinearSeqOptimizedIterableLikeTraversableLikeTraversableOnceGenTraversableOnce
54. #### def filter(p: (A) ⇒ Boolean): Stream[A]

Returns all the elements of this `Stream` that satisfy the predicate `p` in a new `Stream` - i.

Returns all the elements of this `Stream` that satisfy the predicate `p` in a new `Stream` - i.e. it is still a lazy data structure. The order of the elements is preserved

p

the predicate used to filter the stream.

returns

the elements of this stream satisfying `p`.

Definition Classes
StreamTraversableLikeGenTraversableLike
Example:
1. ```def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1)
naturalsFrom(1)  10 } filter { _ % 5 == 0 } take 10 mkString(", ")
// produces
```
55. #### def filterNot(p: (A) ⇒ Boolean): Stream[A]

Selects all elements of this stream which do not satisfy a predicate.

Selects all elements of this stream which do not satisfy a predicate.

p

the predicate used to test elements.

returns

a new stream consisting of all elements of this stream that do not satisfy the given predicate `p`. The order of the elements is preserved.

Definition Classes
TraversableLikeGenTraversableLike
56. #### def finalize(): Unit

Called by the garbage collector on the receiver object when there are no more references to the object.

Called by the garbage collector on the receiver object when there are no more references to the object.

The details of when and if the `finalize` method is invoked, as well as the interaction between `finalize` and non-local returns and exceptions, are all platform dependent.

Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
()
Note

not specified by SLS as a member of AnyRef

57. #### def find(p: (A) ⇒ Boolean): Option[A]

Finds the first element of the stream satisfying a predicate, if any.

Finds the first element of the stream satisfying a predicate, if any.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

an option value containing the first element in the stream that satisfies `p`, or `None` if none exists.

Definition Classes
LinearSeqOptimizedIterableLikeTraversableLikeTraversableOnceGenTraversableOnce
58. #### final def flatMap[B, That](f: (A) ⇒ GenTraversableOnce[B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Applies the given function `f` to each element of this stream, then concatenates the results.

Applies the given function `f` to each element of this stream, then concatenates the results. As with `map` this function does not need to realize the entire `Stream` but continues to keep it as a lazy `Stream`.

B

The element type of the returned collection That.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

f

the function to apply on each element.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

`f(a0) ::: ... ::: f(an)` if this stream is `[a0, ..., an]`.

Definition Classes
Example:
1. ```// Let's create a Stream of Vectors, each of which contains the
// collection of Fibonacci numbers up to the current value.  We
// can then 'flatMap' that Stream.

val fibVec: Stream[Vector[Int]] = Vector(0) #:: Vector(0, 1) #:: fibVec.zip(fibVec.tail).map(n => {
n._2 ++ Vector(n._1.last + n._2.last)
})

fibVec take 5 foreach println
// prints
// Vector(0)
// Vector(0, 1)
// Vector(0, 1, 1)
// Vector(0, 1, 1, 2)
// Vector(0, 1, 1, 2, 3)

// If we now want to `flatMap` across that stream by adding 10
// we can see what the series turns into:

fibVec.flatMap(_.map(_ + 10)) take 15 mkString(", ")
// produces: 10, 10, 11, 10, 11, 11, 10, 11, 11, 12, 10, 11, 11, 12, 13
```
59. #### def flatten[B](implicit asTraversable: (A) ⇒ TraversableOnce[B]): Stream[B]

Evaluates and concatenates all elements within the `Stream` into a new flattened `Stream`.

Evaluates and concatenates all elements within the `Stream` into a new flattened `Stream`.

B

The type of the elements of the resulting `Stream`.

asTraversable

an implicit conversion which asserts that the element type of this stream is a `Traversable`.

returns

A new `Stream` of type `B` of the flattened elements of `this` `Stream`.

Definition Classes
StreamTraversableGenericTraversableTemplate
Example:
1. ```val sov: Stream[Vector[Int]] = Vector(0) #:: Vector(0, 0) #:: sov.zip(sov.tail).map { n => n._1 ++ n._2 }
sov flatten take 10 mkString ", "
// produces: "0, 0, 0, 0, 0, 0, 0, 0, 0, 0"
```
60. #### def fold[A1 >: A](z: A1)(op: (A1, A1) ⇒ A1): A1

Folds the elements of this stream using the specified associative binary operator.

Folds the elements of this stream using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

A1

a type parameter for the binary operator, a supertype of `A`.

z

a neutral element for the fold operation; may be added to the result an arbitrary number of times, and must not change the result (e.g., `Nil` for list concatenation, 0 for addition, or 1 for multiplication.)

op

a binary operator that must be associative

returns

the result of applying fold operator `op` between all the elements and `z`

Definition Classes
TraversableOnceGenTraversableOnce
61. #### final def foldLeft[B](z: B)(op: (B, A) ⇒ B): B

Stream specialization of foldLeft which allows GC to collect along the way.

Stream specialization of foldLeft which allows GC to collect along the way.

B

The type of value being accumulated.

z

The initial value seeded into the function `op`.

op

The operation to perform on successive elements of the `Stream`.

returns

The accumulated value from successive applications of `op`.

Definition Classes
StreamLinearSeqOptimizedTraversableOnceGenTraversableOnce
Annotations
()
62. #### def foldRight[B](z: B)(f: (A, B) ⇒ B): B

Applies a binary operator to all elements of this stream and a start value, going right to left.

Applies a binary operator to all elements of this stream and a start value, going right to left.

Note: will not terminate for infinite-sized collections.

B

the result type of the binary operator.

z

the start value.

returns

the result of inserting `op` between consecutive elements of this stream, going right to left with the start value `z` on the right:

```            op(x1, op(x2, ... op(xn, z)...))
```

where `x1, ..., xn` are the elements of this stream.

Definition Classes
LinearSeqOptimizedIterableLikeTraversableOnceGenTraversableOnce
63. #### def forall(p: (A) ⇒ Boolean): Boolean

Tests whether a predicate holds for all elements of this stream.

Tests whether a predicate holds for all elements of this stream.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

`true` if the given predicate `p` holds for all elements of this stream, otherwise `false`.

Definition Classes
LinearSeqOptimizedIterableLikeTraversableLikeTraversableOnceGenTraversableOnce
64. #### def force: Stream[A]

Forces evaluation of the whole stream and returns it.

Forces evaluation of the whole stream and returns it.

returns

The fully realized `Stream`.

Note

Often we use `Stream`s to represent an infinite set or series. If that's the case for your particular `Stream` then this function will never return and will probably crash the VM with an `OutOfMemory` exception.

65. #### final def foreach[B](f: (A) ⇒ B): Unit

Apply the given function `f` to each element of this linear sequence (while respecting the order of the elements).

Apply the given function `f` to each element of this linear sequence (while respecting the order of the elements).

f

The treatment to apply to each element.

Definition Classes
Annotations
()
Note

This function will force the realization of the entire stream unless the `f` throws an exception.

,

Overridden here as final to trigger tail-call optimization, which replaces 'this' with 'tail' at each iteration. This is absolutely necessary for allowing the GC to collect the underlying stream as elements are consumed.

66. #### def genericBuilder[B]: Builder[B, Stream[B]]

The generic builder that builds instances of Stream at arbitrary element types.

The generic builder that builds instances of Stream at arbitrary element types.

Definition Classes
GenericTraversableTemplate
67. #### final def getClass(): java.lang.Class[_]

A representation that corresponds to the dynamic class of the receiver object.

A representation that corresponds to the dynamic class of the receiver object.

The nature of the representation is platform dependent.

returns

a representation that corresponds to the dynamic class of the receiver object.

Definition Classes
AnyRef → Any
Note

not specified by SLS as a member of AnyRef

68. #### def groupBy[K](f: (A) ⇒ K): Map[K, Stream[A]]

Partitions this stream into a map of streams according to some discriminator function.

Partitions this stream into a map of streams according to some discriminator function.

Note: this method is not re-implemented by views. This means when applied to a view it will always force the view and return a new stream.

K

the type of keys returned by the discriminator function.

f

the discriminator function.

returns

A map from keys to streams such that the following invariant holds:

```                (xs partition f)(k) = xs filter (x => f(x) == k)
```

That is, every key `k` is bound to a stream of those elements `x` for which `f(x)` equals `k`.

Definition Classes
TraversableLikeGenTraversableLike
69. #### def grouped(size: Int): Iterator[Stream[A]]

Partitions elements in fixed size streams.

Partitions elements in fixed size streams.

size

the number of elements per group

returns

An iterator producing streams of size `size`, except the last will be truncated if the elements don't divide evenly.

Definition Classes
IterableLike

Iterator#grouped

70. #### def hasDefiniteSize: Boolean

Tests whether this stream is known to have a finite size.

Tests whether this stream is known to have a finite size. All strict collections are known to have finite size. For a non-strict collection such as `Stream`, the predicate returns `true` if all elements have been computed. It returns `false` if the stream is not yet evaluated to the end.

Note: many collection methods will not work on collections of infinite sizes.

returns

`true` if this collection is known to have finite size, `false` otherwise.

Definition Classes
StreamTraversableLikeTraversableOnceGenTraversableOnce
71. #### def hashCode(): Int

Hashcodes for Stream produce a value from the hashcodes of all the elements of the stream.

Hashcodes for Stream produce a value from the hashcodes of all the elements of the stream.

returns

the hash code value for this object.

Definition Classes
GenSeqLike → AnyRef → Any

Selects the first element of this stream.

Selects the first element of this stream.

returns

the first element of this stream.

Definition Classes
IterableLikeGenIterableLikeTraversableLikeGenTraversableLike
Exceptions thrown
`NoSuchElementException`

if the stream is empty.

Optionally selects the first element.

Optionally selects the first element.

returns

the first element of this stream if it is nonempty, `None` if it is empty.

Definition Classes
TraversableLike
74. #### abstract def indexOf(elem: A, from: Int): Int

[use case] Finds index of first occurrence of some value in this stream after or at some start index.

[use case]

Finds index of first occurrence of some value in this stream after or at some start index.

elem

the element value to search for.

from

the start index

returns

the index `>= from` of the first element of this stream that is equal (wrt `==`) to `elem`, or `-1`, if none exists.

Definition Classes
GenSeqLike
75. #### def indexOf[B >: A](elem: B, from: Int): Int

Finds index of first occurrence of some value in this stream after or at some start index.

Finds index of first occurrence of some value in this stream after or at some start index.

Note: may not terminate for infinite-sized collections.

B

the type of the element `elem`.

elem

the element value to search for.

from

the start index

returns

the index `>= from` of the first element of this stream that is equal (wrt `==`) to `elem`, or `-1`, if none exists.

Definition Classes
GenSeqLike
76. #### abstract def indexOf(elem: A): Int

[use case] Finds index of first occurrence of some value in this stream.

[use case]

Finds index of first occurrence of some value in this stream.

elem

the element value to search for.

returns

the index of the first element of this stream that is equal (wrt `==`) to `elem`, or `-1`, if none exists.

Definition Classes
GenSeqLike
77. #### def indexOf[B >: A](elem: B): Int

Finds index of first occurrence of some value in this stream.

Finds index of first occurrence of some value in this stream.

Note: may not terminate for infinite-sized collections.

B

the type of the element `elem`.

elem

the element value to search for.

returns

the index of the first element of this stream that is equal (wrt `==`) to `elem`, or `-1`, if none exists.

Definition Classes
GenSeqLike
78. #### def indexOfSlice[B >: A](that: GenSeq[B], from: Int): Int

Finds first index after or at a start index where this stream contains a given sequence as a slice.

Finds first index after or at a start index where this stream contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

that

the sequence to test

from

the start index

returns

the first index `>= from` such that the elements of this stream starting at this index match the elements of sequence `that`, or `-1` of no such subsequence exists.

Definition Classes
SeqLike
79. #### def indexOfSlice[B >: A](that: GenSeq[B]): Int

Finds first index where this stream contains a given sequence as a slice.

Finds first index where this stream contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

that

the sequence to test

returns

the first index such that the elements of this stream starting at this index match the elements of sequence `that`, or `-1` of no such subsequence exists.

Definition Classes
SeqLike
80. #### def indexWhere(p: (A) ⇒ Boolean, from: Int): Int

Finds index of the first element satisfying some predicate after or at some start index.

Finds index of the first element satisfying some predicate after or at some start index.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

from

the start index

returns

the index `>= from` of the first element of this stream that satisfies the predicate `p`, or `-1`, if none exists.

Definition Classes
LinearSeqOptimizedSeqLikeGenSeqLike
81. #### def indexWhere(p: (A) ⇒ Boolean): Int

Finds index of first element satisfying some predicate.

Finds index of first element satisfying some predicate.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

the index of the first element of this stream that satisfies the predicate `p`, or `-1`, if none exists.

Definition Classes
GenSeqLike
82. #### def indices: Range

Produces the range of all indices of this sequence.

Produces the range of all indices of this sequence.

returns

a `Range` value from `0` to one less than the length of this stream.

Definition Classes
SeqLike
83. #### def init: Stream[A]

The stream without its last element.

The stream without its last element.

returns

A new `Stream` containing everything but the last element. If your `Stream` represents an infinite series, this method will not return.

Definition Classes
StreamTraversableLike
Exceptions thrown
`Predef.UnsupportedOperationException`

if the stream is empty.

84. #### def inits: Iterator[Stream[A]]

Iterates over the inits of this stream.

Iterates over the inits of this stream. The first value will be this stream and the final one will be an empty stream, with the intervening values the results of successive applications of `init`.

returns

an iterator over all the inits of this stream

Definition Classes
TraversableLike
Example:
1. `List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)`

85. #### abstract def intersect(that: Seq[A]): Stream[A]

[use case] Computes the multiset intersection between this stream and another sequence.

[use case]

Computes the multiset intersection between this stream and another sequence.

Note: may not terminate for infinite-sized collections.

that

the sequence of elements to intersect with.

returns

a new collection of type `That` which contains all elements of this stream which also appear in `that`. If an element value `x` appears n times in `that`, then the first n occurrences of `x` will be retained in the result, but any following occurrences will be omitted.

Definition Classes
SeqLike
86. #### def intersect[B >: A](that: GenSeq[B]): Stream[A]

Computes the multiset intersection between this stream and another sequence.

Computes the multiset intersection between this stream and another sequence.

Note: may not terminate for infinite-sized collections.

B

the element type of the returned stream.

that

the sequence of elements to intersect with.

returns

a new collection of type `That` which contains all elements of this stream which also appear in `that`. If an element value `x` appears n times in `that`, then the first n occurrences of `x` will be retained in the result, but any following occurrences will be omitted.

Definition Classes
SeqLikeGenSeqLike
87. #### def isDefinedAt(x: Int): Boolean

Tests whether this stream contains given index.

Tests whether this stream contains given index.

The implementations of methods `apply` and `isDefinedAt` turn a `Seq[A]` into a `PartialFunction[Int, A]`.

returns

`true` if this stream contains an element at position `idx`, `false` otherwise.

Definition Classes
LinearSeqOptimizedGenSeqLike
88. #### def isEmpty: Boolean

Tests whether the stream is empty.

Tests whether the stream is empty.

returns

`true` if the stream contains no elements, `false` otherwise.

Definition Classes
IterableLikeGenIterableLikeTraversableLikeTraversableOnceGenTraversableOnce
89. #### final def isInstanceOf[T0]: Boolean

Test whether the dynamic type of the receiver object is `T0`.

Test whether the dynamic type of the receiver object is `T0`.

Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression `1.isInstanceOf[String]` will return `false`, while the expression `List(1).isInstanceOf[List[String]]` will return `true`. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

returns

`true` if the receiver object is an instance of erasure of type `T0`; `false` otherwise.

Definition Classes
Any
90. #### final def isTraversableAgain: Boolean

Tests whether this stream can be repeatedly traversed.

Tests whether this stream can be repeatedly traversed.

returns

`true`

Definition Classes
GenTraversableLikeGenTraversableOnce
91. #### def iterator: Iterator[A]

A lazier Iterator than LinearSeqLike's.

A lazier Iterator than LinearSeqLike's.

returns

the new iterator

Definition Classes
StreamLinearSeqLikeIterableLikeGenIterableLike
92. #### def last: A

Selects the last element.

Selects the last element.

returns

The last element of this stream.

Definition Classes
LinearSeqOptimizedTraversableLike
Exceptions thrown
NoSuchElementException

If the stream is empty.

93. #### abstract def lastIndexOf(elem: A, end: Int): Int

[use case] Finds index of last occurrence of some value in this stream before or at a given end index.

[use case]

Finds index of last occurrence of some value in this stream before or at a given end index.

elem

the element value to search for.

end

the end index.

returns

the index `<= end` of the last element of this stream that is equal (wrt `==`) to `elem`, or `-1`, if none exists.

Definition Classes
GenSeqLike
94. #### def lastIndexOf[B >: A](elem: B, end: Int): Int

Finds index of last occurrence of some value in this stream before or at a given end index.

Finds index of last occurrence of some value in this stream before or at a given end index.

B

the type of the element `elem`.

elem

the element value to search for.

end

the end index.

returns

the index `<= end` of the last element of this stream that is equal (wrt `==`) to `elem`, or `-1`, if none exists.

Definition Classes
GenSeqLike
95. #### abstract def lastIndexOf(elem: A): Int

[use case] Finds index of last occurrence of some value in this stream.

[use case]

Finds index of last occurrence of some value in this stream.

elem

the element value to search for.

returns

the index of the last element of this stream that is equal (wrt `==`) to `elem`, or `-1`, if none exists.

Definition Classes
GenSeqLike
96. #### def lastIndexOf[B >: A](elem: B): Int

Finds index of last occurrence of some value in this stream.

Finds index of last occurrence of some value in this stream.

Note: will not terminate for infinite-sized collections.

B

the type of the element `elem`.

elem

the element value to search for.

returns

the index of the last element of this stream that is equal (wrt `==`) to `elem`, or `-1`, if none exists.

Definition Classes
GenSeqLike
97. #### def lastIndexOfSlice[B >: A](that: GenSeq[B], end: Int): Int

Finds last index before or at a given end index where this stream contains a given sequence as a slice.

Finds last index before or at a given end index where this stream contains a given sequence as a slice.

that

the sequence to test

end

the end index

returns

the last index `<= end` such that the elements of this stream starting at this index match the elements of sequence `that`, or `-1` of no such subsequence exists.

Definition Classes
SeqLike
98. #### def lastIndexOfSlice[B >: A](that: GenSeq[B]): Int

Finds last index where this stream contains a given sequence as a slice.

Finds last index where this stream contains a given sequence as a slice.

Note: will not terminate for infinite-sized collections.

that

the sequence to test

returns

the last index such that the elements of this stream starting a this index match the elements of sequence `that`, or `-1` of no such subsequence exists.

Definition Classes
SeqLike
99. #### def lastIndexWhere(p: (A) ⇒ Boolean, end: Int): Int

Finds index of last element satisfying some predicate before or at given end index.

Finds index of last element satisfying some predicate before or at given end index.

p

the predicate used to test elements.

returns

the index `<= end` of the last element of this stream that satisfies the predicate `p`, or `-1`, if none exists.

Definition Classes
LinearSeqOptimizedSeqLikeGenSeqLike
100. #### def lastIndexWhere(p: (A) ⇒ Boolean): Int

Finds index of last element satisfying some predicate.

Finds index of last element satisfying some predicate.

Note: will not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

the index of the last element of this stream that satisfies the predicate `p`, or `-1`, if none exists.

Definition Classes
GenSeqLike
101. #### def lastOption: Option[A]

Optionally selects the last element.

Optionally selects the last element.

returns

the last element of this stream\$ if it is nonempty, `None` if it is empty.

Definition Classes
TraversableLike
102. #### def length: Int

Returns the length of this `Stream`.

Returns the length of this `Stream`.

returns

The length of this `Stream`.

Definition Classes
StreamLinearSeqOptimizedSeqLikeGenSeqLike
Note

In order to compute the length of the `Stream`, it must first be fully realized, which could cause the complete evaluation of an infinite series, assuming that's what your `Stream` represents.

103. #### def lengthCompare(len: Int): Int

Compares the length of this stream to a test value.

Compares the length of this stream to a test value.

len

the test value that gets compared with the length.

returns

A value `x` where

```       x <  0       if this.length <  len
x == 0       if this.length == len
x >  0       if this.length >  len
```

The method as implemented here does not call `length` directly; its running time is `O(length min len)` instead of `O(length)`. The method should be overwritten if computing `length` is cheap.

Definition Classes
LinearSeqOptimizedSeqLike
104. #### def lift: (Int) ⇒ Option[A]

Turns this partial function into an plain function returning an `Option` result.

Turns this partial function into an plain function returning an `Option` result.

returns

a function that takes an argument `x` to `Some(this(x))` if `this` is defined for `x`, and to `None` otherwise.

Definition Classes
PartialFunction

Function.unlift

105. #### final def map[B, That](f: (A) ⇒ B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Returns the stream resulting from applying the given function `f` to each element of this stream.

Returns the stream resulting from applying the given function `f` to each element of this stream. This returns a lazy `Stream` such that it does not need to be fully realized.

B

The element type of the returned collection That.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

f

function to apply to each element.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

`f(a0), ..., f(an)` if this sequence is `a0, ..., an`.

Definition Classes
Example:
1. ```def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1)
naturalsFrom(1).map(_ + 10) take 5 mkString(", ")
// produces: "11, 12, 13, 14, 15"
```
106. #### abstract def max: A

[use case] Finds the largest element.

[use case]

Finds the largest element.

returns

the largest element of this stream with respect to the ordering `cmp`.

Definition Classes
GenTraversableOnce
107. #### def max[B >: A](implicit cmp: Ordering[B]): A

Finds the largest element.

Finds the largest element.

B

The type over which the ordering is defined.

cmp

An ordering to be used for comparing elements.

returns

the largest element of this stream with respect to the ordering `cmp`.

Definition Classes
TraversableOnceGenTraversableOnce
108. #### def maxBy[B](f: (A) ⇒ B)(implicit cmp: Ordering[B]): A

Definition Classes
TraversableOnceGenTraversableOnce
109. #### abstract def min: A

[use case] Finds the smallest element.

[use case]

Finds the smallest element.

returns

the smallest element of this stream with respect to the ordering `cmp`.

Definition Classes
GenTraversableOnce
110. #### def min[B >: A](implicit cmp: Ordering[B]): A

Finds the smallest element.

Finds the smallest element.

B

The type over which the ordering is defined.

cmp

An ordering to be used for comparing elements.

returns

the smallest element of this stream with respect to the ordering `cmp`.

Definition Classes
TraversableOnceGenTraversableOnce
111. #### def minBy[B](f: (A) ⇒ B)(implicit cmp: Ordering[B]): A

Definition Classes
TraversableOnceGenTraversableOnce
112. #### def mkString(start: String, sep: String, end: String): String

Displays all elements of this stream in a string using start, end, and separator strings.

Displays all elements of this stream in a string using start, end, and separator strings.

start

the starting string.

sep

the separator string.

end

the ending string.

returns

a string representation of this stream. The resulting string begins with the string `start` and ends with the string `end`. Inside, the string representations (w.r.t. the method `toString`) of all elements of this stream are separated by the string `sep`.

Definition Classes
StreamTraversableOnceGenTraversableOnce
Example:
1. `List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"`

113. #### def mkString: String

Displays all elements of this stream in a string.

Displays all elements of this stream in a string.

returns

a string representation of this stream. In the resulting string the string representations (w.r.t. the method `toString`) of all elements of this stream follow each other without any separator string.

Definition Classes
StreamTraversableOnceGenTraversableOnce
114. #### def mkString(sep: String): String

Displays all elements of this stream in a string using a separator string.

Displays all elements of this stream in a string using a separator string.

sep

the separator string.

returns

a string representation of this stream. In the resulting string the string representations (w.r.t. the method `toString`) of all elements of this stream are separated by the string `sep`.

Definition Classes
StreamTraversableOnceGenTraversableOnce
Example:
1. `List(1, 2, 3).mkString("|") = "1|2|3"`

115. #### final def ne(arg0: AnyRef): Boolean

Equivalent to `!(this eq that)`.

Equivalent to `!(this eq that)`.

returns

`true` if the argument is not a reference to the receiver object; `false` otherwise.

Definition Classes
AnyRef
116. #### def newBuilder: Builder[A, Stream[A]]

The builder that builds instances of type Stream[A]

The builder that builds instances of type Stream[A]

Attributes
protected[this]
Definition Classes
GenericTraversableTemplateHasNewBuilder
117. #### def nonEmpty: Boolean

Tests whether the stream is not empty.

Tests whether the stream is not empty.

returns

`true` if the stream contains at least one element, `false` otherwise.

Definition Classes
TraversableOnceGenTraversableOnce
118. #### final def notify(): Unit

Wakes up a single thread that is waiting on the receiver object's monitor.

Wakes up a single thread that is waiting on the receiver object's monitor.

Definition Classes
AnyRef
Note

not specified by SLS as a member of AnyRef

119. #### final def notifyAll(): Unit

Wakes up all threads that are waiting on the receiver object's monitor.

Wakes up all threads that are waiting on the receiver object's monitor.

Definition Classes
AnyRef
Note

not specified by SLS as a member of AnyRef

120. #### def orElse[A1 <: Int, B1 >: A](that: PartialFunction[A1, B1]): PartialFunction[A1, B1]

Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

A1

the argument type of the fallback function

B1

the result type of the fallback function

that

the fallback function

returns

a partial function which has as domain the union of the domains of this partial function and `that`. The resulting partial function takes `x` to `this(x)` where `this` is defined, and to `that(x)` where it is not.

Definition Classes
PartialFunction
121. #### def padTo[B >: A, That](len: Int, elem: B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Returns a new sequence of given length containing the elements of this sequence followed by zero or more occurrences of given elements.

Returns a new sequence of given length containing the elements of this sequence followed by zero or more occurrences of given elements.

B

The type of the value to pad with.

That

The type contained within the resulting `Stream`.

len

The number of elements to pad into the `Stream`.

elem

The value of the type `B` to use for padding.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

A new `Stream` representing the collection with values padding off to the end. If your `Stream` represents an infinite series, this method will not return.

Definition Classes
StreamSeqLikeGenSeqLike
Example:
1. ```def naturalsFrom(i: Int): Stream[Int] = i #:: { if (i < 5) naturalsFrom(i + 1) else Stream.Empty }
// prints
// 1
// 2
// 3
// 4
// 5
// 0
// 0
// 0
// 0
// 0
```
122. #### def par: ParSeq[A]

Returns a parallel implementation of this collection.

Returns a parallel implementation of this collection.

For most collection types, this method creates a new parallel collection by copying all the elements. For these collection, `par` takes linear time. Mutable collections in this category do not produce a mutable parallel collection that has the same underlying dataset, so changes in one collection will not be reflected in the other one.

Specific collections (e.g. `ParArray` or `mutable.ParHashMap`) override this default behaviour by creating a parallel collection which shares the same underlying dataset. For these collections, `par` takes constant or sublinear time.

All parallel collections return a reference to themselves.

returns

a parallel implementation of this collection

Definition Classes
Parallelizable
123. #### def parCombiner: Combiner[A, ParSeq[A]]

The default `par` implementation uses the combiner provided by this method to create a new parallel collection.

The default `par` implementation uses the combiner provided by this method to create a new parallel collection.

returns

a combiner for the parallel collection of type `ParRepr`

Attributes
protected[this]
Definition Classes
SeqSeqLikeIterableTraversableLikeParallelizable
124. #### def partition(p: (A) ⇒ Boolean): (Stream[A], Stream[A])

Returns all the elements of this stream that satisfy the predicate `p` returning of Tuple2 of `Stream`s obeying the partition predicate `p`.

Returns all the elements of this stream that satisfy the predicate `p` returning of Tuple2 of `Stream`s obeying the partition predicate `p`. The order of the elements is preserved.

p

the predicate used to filter the stream.

returns

the elements of this stream satisfying `p`.

Definition Classes
StreamTraversableLikeGenTraversableLike
Example:
1. ```def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1)
val parts = naturalsFrom(1) partition { _ % 2 == 0 }
parts._1 take 10 mkString ", "
// produces: "2, 4, 6, 8, 10, 12, 14, 16, 18, 20"
parts._2 take 10 mkString ", "
// produces: "1, 3, 5, 7, 9, 11, 13, 15, 17, 19"
```
125. #### abstract def patch(from: Int, that: GenSeq[A], replaced: Int): Stream[A]

[use case] Produces a new stream where a slice of elements in this stream is replaced by another sequence.

[use case]

Produces a new stream where a slice of elements in this stream is replaced by another sequence.

from

the index of the first replaced element

replaced

the number of elements to drop in the original stream

returns

a new stream consisting of all elements of this stream except that `replaced` elements starting from `from` are replaced by `patch`.

Definition Classes
GenSeqLike
126. #### def patch[B >: A, That](from: Int, patch: GenSeq[B], replaced: Int)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Produces a new stream where a slice of elements in this stream is replaced by another sequence.

Produces a new stream where a slice of elements in this stream is replaced by another sequence.

B

the element type of the returned stream.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

from

the index of the first replaced element

patch

the replacement sequence

replaced

the number of elements to drop in the original stream

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new stream consisting of all elements of this stream except that `replaced` elements starting from `from` are replaced by `patch`.

Definition Classes
SeqLikeGenSeqLike
127. #### def permutations: Iterator[Stream[A]]

Iterates over distinct permutations.

Iterates over distinct permutations.

returns

An Iterator which traverses the distinct permutations of this stream.

Definition Classes
SeqLike
Example:
1. `"abb".permutations = Iterator(abb, bab, bba)`

128. #### def prefixLength(p: (A) ⇒ Boolean): Int

Returns the length of the longest prefix whose elements all satisfy some predicate.

Returns the length of the longest prefix whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

the length of the longest prefix of this stream such that every element of the segment satisfies the predicate `p`.

Definition Classes
GenSeqLike
129. #### def print(sep: String): Unit

Prints elements of this stream one by one, separated by `sep`.

Prints elements of this stream one by one, separated by `sep`.

sep

The separator string printed between consecutive elements.

130. #### def print(): Unit

Prints elements of this stream one by one, separated by commas.

131. #### abstract def product: A

[use case] Multiplies up the elements of this collection.

[use case]

Multiplies up the elements of this collection.

returns

the product of all elements of this stream with respect to the `*` operator in `num`.

Definition Classes
GenTraversableOnce
132. #### def product[B >: A](implicit num: Numeric[B]): B

Multiplies up the elements of this collection.

Multiplies up the elements of this collection.

B

the result type of the `*` operator.

num

an implicit parameter defining a set of numeric operations which includes the `*` operator to be used in forming the product.

returns

the product of all elements of this stream with respect to the `*` operator in `num`.

Definition Classes
TraversableOnceGenTraversableOnce
133. #### def reduce[A1 >: A](op: (A1, A1) ⇒ A1): A1

Reduces the elements of this stream using the specified associative binary operator.

Reduces the elements of this stream using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

A1

A type parameter for the binary operator, a supertype of `A`.

op

A binary operator that must be associative.

returns

The result of applying reduce operator `op` between all the elements if the stream is nonempty.

Definition Classes
TraversableOnceGenTraversableOnce
Exceptions thrown
UnsupportedOperationException

if this stream is empty.

134. #### final def reduceLeft[B >: A](f: (B, A) ⇒ B): B

Stream specialization of reduceLeft which allows GC to collect along the way.

Stream specialization of reduceLeft which allows GC to collect along the way.

B

The type of value being accumulated.

f

The operation to perform on successive elements of the `Stream`.

returns

The accumulated value from successive applications of `f`.

Definition Classes
StreamLinearSeqOptimizedTraversableOnce
135. #### def reduceLeftOption[B >: A](op: (B, A) ⇒ B): Option[B]

Optionally applies a binary operator to all elements of this stream, going left to right.

Optionally applies a binary operator to all elements of this stream, going left to right.

Note: will not terminate for infinite-sized collections.

B

the result type of the binary operator.

op

the binary operator.

returns

an option value containing the result of `reduceLeft(op)` is this stream is nonempty, `None` otherwise.

Definition Classes
TraversableOnceGenTraversableOnce
136. #### def reduceOption[A1 >: A](op: (A1, A1) ⇒ A1): Option[A1]

Reduces the elements of this stream, if any, using the specified associative binary operator.

Reduces the elements of this stream, if any, using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

A1

A type parameter for the binary operator, a supertype of `A`.

op

A binary operator that must be associative.

returns

An option value containing result of applying reduce operator `op` between all the elements if the collection is nonempty, and `None` otherwise.

Definition Classes
TraversableOnceGenTraversableOnce
137. #### def reduceRight[B >: A](op: (A, B) ⇒ B): B

Applies a binary operator to all elements of this stream, going right to left.

Applies a binary operator to all elements of this stream, going right to left.

Note: will not terminate for infinite-sized collections.

B

the result type of the binary operator.

op

the binary operator.

returns

the result of inserting `op` between consecutive elements of this stream, going right to left:

```            op(x,,1,,, op(x,,2,,, ..., op(x,,n-1,,, x,,n,,)...))
```

where `x1, ..., xn` are the elements of this stream.

Definition Classes
LinearSeqOptimizedIterableLikeTraversableOnceGenTraversableOnce
Exceptions thrown
`UnsupportedOperationException`

if this stream is empty.

138. #### def reduceRightOption[B >: A](op: (A, B) ⇒ B): Option[B]

Optionally applies a binary operator to all elements of this stream, going right to left.

Optionally applies a binary operator to all elements of this stream, going right to left.

Note: will not terminate for infinite-sized collections.

B

the result type of the binary operator.

op

the binary operator.

returns

an option value containing the result of `reduceRight(op)` is this stream is nonempty, `None` otherwise.

Definition Classes
TraversableOnceGenTraversableOnce
139. #### def repr: Stream[A]

The collection of type stream underlying this `TraversableLike` object.

The collection of type stream underlying this `TraversableLike` object. By default this is implemented as the `TraversableLike` object itself, but this can be overridden.

Definition Classes
TraversableLikeGenTraversableLike
140. #### def reverse: Stream[A]

A list consisting of all elements of this list in reverse order.

A list consisting of all elements of this list in reverse order.

returns

A new `Stream` containing the representing of the original `Stream` in reverse order.

Definition Classes
StreamSeqLikeGenSeqLike
Example:
1. ```def naturalsFrom(i: Int): Stream[Int] = i #:: { if (i < 5) naturalsFrom(i + 1) else Stream.Empty }
(naturalsFrom(1) reverse) foreach println
// prints
// 5
// 4
// 3
// 2
// 1
```
Note

This function must realize the entire `Stream` in order to perform this operation so if your `Stream` represents an infinite sequence then this function will never return.

141. #### def reverseIterator: Iterator[A]

An iterator yielding elements in reversed order.

An iterator yielding elements in reversed order.

Note: will not terminate for infinite-sized collections.

Note: `xs.reverseIterator` is the same as `xs.reverse.iterator` but might be more efficient.

returns

an iterator yielding the elements of this stream in reversed order

Definition Classes
SeqLike
142. #### abstract def reverseMap[B](f: (A) ⇒ B): Stream[B]

[use case] Builds a new collection by applying a function to all elements of this stream and collecting the results in reversed order.

[use case]

Builds a new collection by applying a function to all elements of this stream and collecting the results in reversed order.

B

the element type of the returned collection.

f

the function to apply to each element.

returns

a new collection of type `That` resulting from applying the given function `f` to each element of this stream and collecting the results in reversed order.

Note: `xs.reverseMap(f)` is the same as `xs.reverse.map(f)` but might be more efficient.

Definition Classes
GenSeqLike
143. #### def reverseMap[B, That](f: (A) ⇒ B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Builds a new collection by applying a function to all elements of this stream and collecting the results in reversed order.

Builds a new collection by applying a function to all elements of this stream and collecting the results in reversed order.

Note: will not terminate for infinite-sized collections.

Note: `xs.reverseMap(f)` is the same as `xs.reverse.map(f)` but might be more efficient.

B

the element type of the returned collection.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

f

the function to apply to each element.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new collection of type `That` resulting from applying the given function `f` to each element of this stream and collecting the results in reversed order.

Definition Classes
SeqLikeGenSeqLike
144. #### def reversed: List[A]

Attributes
protected[this]
Definition Classes
TraversableOnce
145. #### abstract def sameElements(that: GenIterable[A]): Boolean

[use case] Checks if the other iterable collection contains the same elements in the same order as this stream.

[use case]

Checks if the other iterable collection contains the same elements in the same order as this stream.

that

the collection to compare with.

returns

`true`, if both collections contain the same elements in the same order, `false` otherwise.

Definition Classes
GenIterableLike
146. #### def sameElements[B >: A](that: GenIterable[B]): Boolean

Checks if the other iterable collection contains the same elements in the same order as this stream.

Checks if the other iterable collection contains the same elements in the same order as this stream.

Note: will not terminate for infinite-sized collections.

B

the type of the elements of collection `that`.

that

the collection to compare with.

returns

`true`, if both collections contain the same elements in the same order, `false` otherwise.

Definition Classes
LinearSeqOptimizedIterableLikeGenIterableLike
147. #### def scan[B >: A, That](z: B)(op: (B, B) ⇒ B)(implicit cbf: CanBuildFrom[Stream[A], B, That]): That

Computes a prefix scan of the elements of the collection.

Computes a prefix scan of the elements of the collection.

Note: The neutral element `z` may be applied more than once.

B

element type of the resulting collection

That

type of the resulting collection

z

neutral element for the operator `op`

op

the associative operator for the scan

cbf

combiner factory which provides a combiner

returns

a new stream containing the prefix scan of the elements in this stream

Definition Classes
TraversableLikeGenTraversableLike
148. #### final def scanLeft[B, That](z: B)(op: (B, A) ⇒ B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Create a new stream which contains all intermediate results of applying the operator to subsequent elements left to right.

Create a new stream which contains all intermediate results of applying the operator to subsequent elements left to right. `scanLeft` is analogous to `foldLeft`.

B

the type of the elements in the resulting collection

That

the actual type of the resulting collection

z

The initial value for the scan.

op

A function that will apply operations to successive values in the `Stream` against previous accumulated results.

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

A new collection containing the modifications from the application of `op`.

Definition Classes
StreamTraversableLikeGenTraversableLike
Note

This works because the target type of the Builder `That` is a `Stream`.

149. #### def scanRight[B, That](z: B)(op: (A, B) ⇒ B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Produces a collection containing cummulative results of applying the operator going right to left.

Produces a collection containing cummulative results of applying the operator going right to left. The head of the collection is the last cummulative result.

Note: will not terminate for infinite-sized collections.

Example:

```   List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
```
B

the type of the elements in the resulting collection

That

the actual type of the resulting collection

z

the initial value

op

the binary operator applied to the intermediate result and the element

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

collection with intermediate results

Definition Classes
TraversableLikeGenTraversableLike
Annotations
@migration
Migration

(Changed in version 2.9.0) The behavior of `scanRight` has changed. The previous behavior can be reproduced with scanRight.reverse.

150. #### def segmentLength(p: (A) ⇒ Boolean, from: Int): Int

Computes length of longest segment whose elements all satisfy some predicate.

Computes length of longest segment whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

from

the index where the search starts.

returns

the length of the longest segment of this stream starting from index `from` such that every element of the segment satisfies the predicate `p`.

Definition Classes
LinearSeqOptimizedSeqLikeGenSeqLike
151. #### def seq: Seq[A]

A version of this collection with all of the operations implemented sequentially (i.

A version of this collection with all of the operations implemented sequentially (i.e. in a single-threaded manner).

This method returns a reference to this collection. In parallel collections, it is redefined to return a sequential implementation of this collection. In both cases, it has O(1) complexity.

returns

a sequential view of the collection.

Definition Classes
SeqSeqGenSeqIterableIterableGenIterableTraversableTraversableGenTraversableParallelizableTraversableOnceGenTraversableOnce
152. #### def size: Int

The size of this stream, equivalent to `length`.

The size of this stream, equivalent to `length`.

Note: will not terminate for infinite-sized collections.

returns

the number of elements in this stream.

Definition Classes
SeqLikeGenTraversableLikeTraversableOnceGenTraversableOnce
153. #### def slice(from: Int, until: Int): Stream[A]

A substream starting at index `from` and extending up to (but not including) index `until`.

A substream starting at index `from` and extending up to (but not including) index `until`. This returns a `Stream` that is lazily evaluated.

from

the lowest index to include from this stream.

until

the highest index to EXCLUDE from this stream.

returns

A new string containing the elements requested from `start` until `end`.

Definition Classes
StreamLinearSeqOptimizedIterableLikeTraversableLikeGenTraversableLike
Example:
1. ```naturalsFrom(0) slice(50, 60) mkString ", "
// produces: "50, 51, 52, 53, 54, 55, 56, 57, 58, 59"
```
154. #### def sliding[B >: A](size: Int, step: Int): Iterator[Stream[A]]

Definition Classes
IterableLike
155. #### def sliding[B >: A](size: Int): Iterator[Stream[A]]

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)

size

the number of elements per group

returns

An iterator producing streams of size `size`, except the last and the only element will be truncated if there are fewer elements than size.

Definition Classes
IterableLike

Iterator#sliding

156. #### def sortBy[B](f: (A) ⇒ B)(implicit ord: Ordering[B]): Stream[A]

Sorts this Stream according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.

Sorts this Stream according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.

B

the target type of the transformation `f`, and the type where the ordering `ord` is defined.

f

the transformation function mapping elements to some other domain `B`.

ord

the ordering assumed on domain `B`.

returns

a stream consisting of the elements of this stream sorted according to the ordering where `x < y` if `ord.lt(f(x), f(y))`.

Definition Classes
SeqLike
Example:
1. ```   val words = "The quick brown fox jumped over the lazy dog".split(' ')
// this works because scala.Ordering will implicitly provide an Ordering[Tuple2[Int, Char]]
res0: Array[String] = Array(The, dog, fox, the, lazy, over, brown, quick, jumped)
```

scala.math.Ordering

Note: will not terminate for infinite-sized collections.

157. #### def sortWith(lt: (A, A) ⇒ Boolean): Stream[A]

Sorts this stream according to a comparison function.

Sorts this stream according to a comparison function.

Note: will not terminate for infinite-sized collections.

The sort is stable. That is, elements that are equal wrt `lt` appear in the same order in the sorted sequence as in the original.

lt

the comparison function which tests whether its first argument precedes its second argument in the desired ordering.

returns

a stream consisting of the elements of this stream sorted according to the comparison function `lt`.

Definition Classes
SeqLike
Example:
1. ```   List("Steve", "Tom", "John", "Bob").sortWith(_.compareTo(_) < 0) =
List("Bob", "John", "Steve", "Tom")
```
158. #### def sorted[B >: A](implicit ord: Ordering[B]): Stream[A]

Sorts this stream according to an Ordering.

Sorts this stream according to an Ordering.

The sort is stable. That is, elements that are equal wrt `lt` appear in the same order in the sorted sequence as in the original.

ord

the ordering to be used to compare elements.

returns

a stream consisting of the elements of this stream sorted according to the ordering `ord`.

Definition Classes
SeqLike

scala.math.Ordering

159. #### def span(p: (A) ⇒ Boolean): (Stream[A], Stream[A])

Splits this stream into a prefix/suffix pair according to a predicate.

Splits this stream into a prefix/suffix pair according to a predicate.

Note: `c span p` is equivalent to (but possibly more efficient than) `(c takeWhile p, c dropWhile p)`, provided the evaluation of the predicate `p` does not cause any side-effects.

p

the test predicate

returns

a pair consisting of the longest prefix of this stream whose elements all satisfy `p`, and the rest of this stream.

Definition Classes
LinearSeqOptimizedTraversableLikeGenTraversableLike
160. #### def splitAt(n: Int): (Stream[A], Stream[A])

Splits this stream into two at a given position.

Splits this stream into two at a given position. Note: `c splitAt n` is equivalent to (but possibly more efficient than) `(c take n, c drop n)`.

n

the position at which to split.

returns

a pair of streams consisting of the first `n` elements of this stream, and the other elements.

Definition Classes
StreamTraversableLikeGenTraversableLike
161. #### def startsWith[B](that: GenSeq[B], offset: Int): Boolean

Tests whether this stream contains the given sequence at a given index.

Tests whether this stream contains the given sequence at a given index.

If the both the receiver object, `this` and the argument, `that` are infinite sequences this method may not terminate.

that

the sequence to test

offset

the index where the sequence is searched.

returns

`true` if the sequence `that` is contained in this stream at index `offset`, otherwise `false`.

Definition Classes
SeqLikeGenSeqLike
162. #### def startsWith[B](that: GenSeq[B]): Boolean

Tests whether this stream starts with the given sequence.

Tests whether this stream starts with the given sequence.

that

the sequence to test

returns

`true` if this collection has `that` as a prefix, `false` otherwise.

Definition Classes
GenSeqLike
163. #### def stringPrefix: String

Defines the prefix of this object's `toString` representation as `Stream`.

Defines the prefix of this object's `toString` representation as `Stream`.

returns

a string representation which starts the result of `toString` applied to this stream. By default the string prefix is the simple name of the collection class stream.

Definition Classes
StreamTraversableLikeGenTraversableLike
164. #### abstract def sum: A

[use case] Sums up the elements of this collection.

[use case]

Sums up the elements of this collection.

returns

the sum of all elements of this stream with respect to the `+` operator in `num`.

Definition Classes
GenTraversableOnce
165. #### def sum[B >: A](implicit num: Numeric[B]): B

Sums up the elements of this collection.

Sums up the elements of this collection.

B

the result type of the `+` operator.

num

an implicit parameter defining a set of numeric operations which includes the `+` operator to be used in forming the sum.

returns

the sum of all elements of this stream with respect to the `+` operator in `num`.

Definition Classes
TraversableOnceGenTraversableOnce
166. #### final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
167. #### def tail: Stream[A]

Selects all elements except the first.

Selects all elements except the first.

returns

a stream consisting of all elements of this stream except the first one.

Definition Classes
TraversableLikeGenTraversableLike
Exceptions thrown
`UnsupportedOperationException`

if the stream is empty.

168. #### def tails: Iterator[Stream[A]]

Iterates over the tails of this stream.

Iterates over the tails of this stream. The first value will be this stream and the final one will be an empty stream, with the intervening values the results of successive applications of `tail`.

returns

an iterator over all the tails of this stream

Definition Classes
TraversableLike
Example:
1. `List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)`

169. #### def take(n: Int): Stream[A]

Returns the `n` first elements of this `Stream` as another `Stream`, or else the whole `Stream`, if it has less than `n` elements.

Returns the `n` first elements of this `Stream` as another `Stream`, or else the whole `Stream`, if it has less than `n` elements.

The result of `take` is, again, a `Stream` meaning that it also does not make any needless evaluations of the `Stream` itself, delaying that until the usage of the resulting `Stream`.

n

the number of elements to take.

returns

the `n` first elements of this stream.

Definition Classes
StreamLinearSeqOptimizedIterableLikeTraversableLikeGenTraversableLike
Example:
1. ```def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1)
scala> naturalsFrom(5) take 5
res1: scala.collection.immutable.Stream[Int] = Stream(5, ?)

scala> naturalsFrom(5) take 5 mkString ", "
// produces: "5, 6, 7, 8, 9"
```
170. #### def takeRight(n: Int): Stream[A]

Returns the rightmost `n` elements from this iterable.

Returns the rightmost `n` elements from this iterable.

n

the number of elements to take

returns

The last `n` elements from this `Stream`.

Definition Classes
StreamIterableLike
Note

Take serious caution here. If the `Stream` represents an infinite series then this function will not return. The right most elements of an infinite series takes an infinite amount of time to produce.

171. #### def takeWhile(p: (A) ⇒ Boolean): Stream[A]

Returns the longest prefix of this `Stream` whose elements satisfy the predicate `p`.

Returns the longest prefix of this `Stream` whose elements satisfy the predicate `p`.

p

the test predicate.

returns

A new `Stream` representing the values that satisfy the predicate `p`.

Definition Classes
StreamLinearSeqOptimizedIterableLikeTraversableLikeGenTraversableLike
Example:
1. ```naturalsFrom(0) takeWhile { _ < 5 } mkString ", "
produces: "0, 1, 2, 3, 4"
```
172. #### def thisCollection: LinearSeq[A]

The underlying collection seen as an instance of `Stream`.

The underlying collection seen as an instance of `Stream`. By default this is implemented as the current collection object itself, but this can be overridden.

Attributes
protected[this]
Definition Classes
LinearSeqLikeSeqLikeIterableLikeTraversableLike
173. #### abstract def toArray: Array[A]

[use case] Converts this stream to an array.

[use case]

Converts this stream to an array.

Note: will not terminate for infinite-sized collections.

returns

an array containing all elements of this stream.

Definition Classes
GenTraversableOnce
174. #### def toArray[B >: A](implicit arg0: ClassManifest[B]): Array[B]

Converts this stream to an array.

Converts this stream to an array.

Note: will not terminate for infinite-sized collections.

B

the type of the elements of the array. A `ClassManifest` for this type must be available.

returns

an array containing all elements of this stream.

Definition Classes
TraversableOnceGenTraversableOnce
175. #### def toBuffer[B >: A]: Buffer[B]

Converts this stream to a mutable buffer.

Converts this stream to a mutable buffer.

Note: will not terminate for infinite-sized collections.

returns

a buffer containing all elements of this stream.

Definition Classes
TraversableOnceGenTraversableOnce
176. #### def toCollection(repr: Stream[A]): LinearSeq[A]

A conversion from collections of type `Repr` to `Stream` objects.

A conversion from collections of type `Repr` to `Stream` objects. By default this is implemented as just a cast, but this can be overridden.

Attributes
protected[this]
Definition Classes
LinearSeqLikeSeqLikeIterableLikeTraversableLike
177. #### def toIndexedSeq[B >: A]: IndexedSeq[B]

Converts this stream to an indexed sequence.

Converts this stream to an indexed sequence.

Note: will not terminate for infinite-sized collections.

returns

an indexed sequence containing all elements of this stream.

Definition Classes
TraversableOnceGenTraversableOnce
178. #### def toIterable: Iterable[A]

Converts this stream to an iterable collection.

Converts this stream to an iterable collection. Note that the choice of target `Iterable` is lazy in this default implementation as this `TraversableOnce` may be lazy and unevaluated (i.e. it may be an iterator which is only traversable once).

Note: will not terminate for infinite-sized collections.

returns

an `Iterable` containing all elements of this stream.

Definition Classes
IterableLikeTraversableOnceGenTraversableOnce
179. #### def toIterator: Iterator[A]

Returns an Iterator over the elements in this stream.

Returns an Iterator over the elements in this stream. Will return the same Iterator if this instance is already an Iterator.

Note: will not terminate for infinite-sized collections.

returns

an Iterator containing all elements of this stream.

Definition Classes
TraversableLikeGenTraversableOnce
180. #### def toList: List[A]

Converts this stream to a list.

Converts this stream to a list.

Note: will not terminate for infinite-sized collections.

returns

a list containing all elements of this stream.

Definition Classes
TraversableOnceGenTraversableOnce
181. #### abstract def toMap[T, U]: Map[T, U]

[use case] Converts this stream to a map.

[use case]

Converts this stream to a map. This method is unavailable unless the elements are members of Tuple2, each ((T, U)) becoming a key-value pair in the map. Duplicate keys will be overwritten by later keys: if this is an unordered collection, which key is in the resulting map is undefined.

Note: will not terminate for infinite-sized collections.

returns

a map containing all elements of this stream.

Definition Classes
GenTraversableOnce
182. #### def toMap[T, U](implicit ev: <:<[A, (T, U)]): Map[T, U]

Converts this stream to a map.

Converts this stream to a map. This method is unavailable unless the elements are members of Tuple2, each ((T, U)) becoming a key-value pair in the map. Duplicate keys will be overwritten by later keys: if this is an unordered collection, which key is in the resulting map is undefined.

Note: will not terminate for infinite-sized collections.

returns

a map containing all elements of this stream.

Definition Classes
TraversableOnceGenTraversableOnce
183. #### def toSeq: Seq[A]

Converts this stream to a sequence.

Converts this stream to a sequence.

Note: will not terminate for infinite-sized collections.

Overridden for efficiency.

returns

a sequence containing all elements of this stream.

Definition Classes
SeqSeqLikeGenSeqLikeTraversableOnceGenTraversableOnce
184. #### def toSet[B >: A]: Set[B]

Converts this stream to a set.

Converts this stream to a set.

Note: will not terminate for infinite-sized collections.

returns

a set containing all elements of this stream.

Definition Classes
TraversableOnceGenTraversableOnce
185. #### def toStream: Stream[A]

Converts this stream to a stream.

Converts this stream to a stream.

Note: will not terminate for infinite-sized collections.

returns

a stream containing all elements of this stream.

Definition Classes
StreamIterableLikeTraversableLikeGenTraversableOnce
186. #### def toString(): String

Converts this stream to a string.

Converts this stream to a string.

returns

a string representation of this collection. By default this string consists of the `stringPrefix` of this stream, followed by all elements separated by commas and enclosed in parentheses.

Definition Classes
StreamSeqLikeFunction1TraversableLike → AnyRef → Any
187. #### def toTraversable: Traversable[A]

Converts this stream to an unspecified Traversable.

Converts this stream to an unspecified Traversable. Will return the same collection if this instance is already Traversable.

Note: will not terminate for infinite-sized collections.

returns

a Traversable containing all elements of this stream.

Definition Classes
TraversableLikeTraversableOnceGenTraversableOnce
188. #### def transpose[B](implicit asTraversable: (A) ⇒ GenTraversableOnce[B]): Stream[Stream[B]]

Transposes this stream of traversable collections into a stream of streams.

Transposes this stream of traversable collections into a stream of streams.

B

the type of the elements of each traversable collection.

asTraversable

an implicit conversion which asserts that the element type of this stream is a `Traversable`.

returns

a two-dimensional stream of streams which has as nth row the nth column of this stream.

Definition Classes
GenericTraversableTemplate
Annotations
@migration
Migration

(Changed in version 2.9.0) `transpose` throws an `IllegalArgumentException` if collections are not uniformly sized.

Exceptions thrown
`IllegalArgumentException`

if all collections in this stream are not of the same size.

189. #### abstract def union(that: Seq[A]): Stream[A]

[use case] Produces a new sequence which contains all elements of this stream and also all elements of a given sequence.

[use case]

Produces a new sequence which contains all elements of this stream and also all elements of a given sequence. `xs union ys` is equivalent to `xs ++ ys`.

Note: will not terminate for infinite-sized collections.

that

returns

a new collection of type `That` which contains all elements of this stream followed by all elements of `that`.

Definition Classes
SeqLike
190. #### def union[B >: A, That](that: GenSeq[B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That

Produces a new sequence which contains all elements of this stream and also all elements of a given sequence.

Produces a new sequence which contains all elements of this stream and also all elements of a given sequence. `xs union ys` is equivalent to `xs ++ ys`.

Note: will not terminate for infinite-sized collections.

Another way to express this is that `xs union ys` computes the order-presevring multi-set union of `xs` and `ys`. `union` is hence a counter-part of `diff` and `intersect` which also work on multi-sets.

Note: will not terminate for infinite-sized collections.

B

the element type of the returned stream.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

that

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new collection of type `That` which contains all elements of this stream followed by all elements of `that`.

Definition Classes
SeqLikeGenSeqLike
191. #### def unzip[A1, A2](implicit asPair: (A) ⇒ (A1, A2)): (Stream[A1], Stream[A2])

Converts this stream of pairs into two collections of the first and second half of each pair.

Converts this stream of pairs into two collections of the first and second half of each pair.

asPair

an implicit conversion which asserts that the element type of this stream is a pair.

returns

a pair streams, containing the first, respectively second half of each element pair of this stream.

Definition Classes
GenericTraversableTemplate
192. #### def unzip3[A1, A2, A3](implicit asTriple: (A) ⇒ (A1, A2, A3)): (Stream[A1], Stream[A2], Stream[A3])

Converts this stream of triples into three collections of the first, second, and third element of each triple.

Converts this stream of triples into three collections of the first, second, and third element of each triple.

asTriple

an implicit conversion which asserts that the element type of this stream is a triple.

returns

a triple streams, containing the first, second, respectively third member of each element triple of this stream.

Definition Classes
GenericTraversableTemplate
193. #### abstract def updated(index: Int, elem: A): Stream[A]

[use case] A copy of this stream with one single replaced element.

[use case]

A copy of this stream with one single replaced element.

index

the position of the replacement

elem

the replacing element

returns

a new stream` which is a copy of this stream with the element at position `index` replaced by `elem```. ```

Definition Classes
GenSeqLike
194. #### def updated[B >: A, That](index: Int, elem: B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That

A copy of this stream with one single replaced element.

A copy of this stream with one single replaced element.

B

the element type of the returned stream.

That

the class of the returned collection. Where possible, `That` is the same class as the current collection class `Repr`, but this depends on the element type `B` being admissible for that class, which means that an implicit instance of type `CanBuildFrom[Repr, B, That]` is found.

index

the position of the replacement

elem

the replacing element

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `B`.

returns

a new stream` which is a copy of this stream with the element at position `index` replaced by `elem```. ```

Definition Classes
SeqLikeGenSeqLike
195. #### def view: StreamView[A, Stream[A]]

Creates a non-strict view of this stream.

Creates a non-strict view of this stream.

returns

a non-strict view of this stream.

Definition Classes
StreamSeqLikeIterableLikeTraversableLike
196. #### def view(from: Int, until: Int): SeqView[A, Stream[A]]

Creates a non-strict view of a slice of this stream.

Creates a non-strict view of a slice of this stream.

Note: the difference between `view` and `slice` is that `view` produces a view of the current stream, whereas `slice` produces a new stream.

Note: `view(from, to)` is equivalent to `view.slice(from, to)`

from

the index of the first element of the view

until

the index of the element following the view

returns

a non-strict view of a slice of this stream, starting at index `from` and extending up to (but not including) index `until`.

Definition Classes
SeqLikeIterableLikeTraversableLike
197. #### final def wait(): Unit

Definition Classes
AnyRef
Annotations
()
198. #### final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
()
199. #### final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
()
200. #### final def withFilter(p: (A) ⇒ Boolean): StreamWithFilter

Creates a non-strict filter of this stream.

Creates a non-strict filter of this stream.

Note: the difference between `c filter p` and `c withFilter p` is that the former creates a new collection, whereas the latter only restricts the domain of subsequent `map`, `flatMap`, `foreach`, and `withFilter` operations.

p

the predicate used to test elements.

returns

an object of class `WithFilter`, which supports `map`, `flatMap`, `foreach`, and `withFilter` operations. All these operations apply to those elements of this stream which satisfy the predicate `p`.

Definition Classes
201. #### final def zip[A1 >: A, B, That](that: GenIterable[B])(implicit bf: CanBuildFrom[Stream[A], (A1, B), That]): That

Returns a stream formed from this stream and the specified stream `that` by associating each element of the former with the element at the same position in the latter.

Returns a stream formed from this stream and the specified stream `that` by associating each element of the former with the element at the same position in the latter.

If one of the two streams is longer than the other, its remaining elements are ignored.

The return type of this function may not be obvious. The lazy aspect of the returned value is different than that of `partition`. In `partition` we get back a Tuple2 of two lazy `Stream`s whereas here we get back a single lazy `Stream` of Tuple2s where the Tuple2's type signature is `(A1, B)`.

A1

The type of the first parameter of the zipped tuple

B

The type of the second parameter of the zipped tuple

That

The type of the returned `Stream`.

that

The iterable providing the second half of each result pair

bf

an implicit value of class `CanBuildFrom` which determines the result class `That` from the current representation type `Repr` and the new element type `(A1, B)`.

returns

```Stream({a0,b0}, ..., {amin(m,n),bmin(m,n))}``` when ```Stream(a0, ..., am) zip Stream(b0, ..., bn)``` is invoked.

Definition Classes
StreamIterableLikeGenIterableLike
Example:
1. ```def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1)
naturalsFrom(1) zip naturalsFrom(2) zip take 5 foreach println
// prints
// (1,2)
// (2,3)
// (3,4)
// (4,5)
// (5,6)
```
202. #### abstract def zipAll[B](that: Iterable[B], thisElem: A, thatElem: B): Stream[(A, B)]

[use case] Returns a stream formed from this stream and another iterable collection by combining corresponding elements in pairs.

[use case]

Returns a stream formed from this stream and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.

that

the iterable providing the second half of each result pair

thisElem

the element to be used to fill up the result if this stream is shorter than `that`.

thatElem

the element to be used to fill up the result if `that` is shorter than this stream.

returns

a new collection of type `That` containing pairs consisting of corresponding elements of this stream and `that`. The length of the returned collection is the maximum of the lengths of this stream and `that`. If this stream is shorter than `that`, `thisElem` values are used to pad the result. If `that` is shorter than this stream, `thatElem` values are used to pad the result.

Definition Classes
GenIterableLike
203. #### def zipAll[B, A1 >: A, That](that: GenIterable[B], thisElem: A1, thatElem: B)(implicit bf: CanBuildFrom[Stream[A], (A1, B), That]): That

Returns a stream formed from this stream and another iterable collection by combining corresponding elements in pairs.

Returns a stream formed from this stream and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.

that

the iterable providing the second half of each result pair

thisElem

the element to be used to fill up the result if this stream is shorter than `that`.

thatElem

the element to be used to fill up the result if `that` is shorter than this stream.

returns

a new collection of type `That` containing pairs consisting of corresponding elements of this stream and `that`. The length of the returned collection is the maximum of the lengths of this stream and `that`. If this stream is shorter than `that`, `thisElem` values are used to pad the result. If `that` is shorter than this stream, `thatElem` values are used to pad the result.

Definition Classes
IterableLikeGenIterableLike
204. #### def zipWithIndex[A1 >: A, That](implicit bf: CanBuildFrom[Stream[A], (A1, Int), That]): That

Zips this iterable with its indices.

Zips this iterable with its indices. `s.zipWithIndex` is equivalent to ```s zip s.indices```.

This method is much like `zip` in that it returns a single lazy `Stream` of Tuple2.

A1

The type of the first element of the Tuple2 in the resulting stream.

That

The type of the resulting `Stream`.

returns

`Stream({a0,0}, ..., {an,n)}`

Definition Classes
StreamIterableLikeGenIterableLike
Example:
1. ```def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1)
(naturalsFrom(1) zipWithIndex) take 5 foreach println
// prints
// (1,0)
// (2,1)
// (3,2)
// (4,3)
// (5,4)
```

### Deprecated Value Members

1. #### def elements: Iterator[A]

Definition Classes
IterableLike
Annotations
Deprecated

(Since version 2.8.0) use `iterator' instead`

2. #### def equalsWith[B](that: Seq[B])(f: (A, B) ⇒ Boolean): Boolean

Tests whether every element of this stream relates to the corresponding element of another sequence by satisfying a test predicate.

Tests whether every element of this stream relates to the corresponding element of another sequence by satisfying a test predicate.

B

the type of the elements of `that`

that

the other sequence

returns

`true` if both sequences have the same length and `p(x, y)` is `true` for all corresponding elements `x` of this stream and `y` of `that`, otherwise `false`.

Definition Classes
SeqLike
Annotations
Deprecated

(Since version 2.8.0) use `corresponds` instead

3. #### def findIndexOf(p: (A) ⇒ Boolean): Int

Returns index of the first element satisfying a predicate, or `-1`.

Returns index of the first element satisfying a predicate, or `-1`.

Definition Classes
SeqLike
Annotations
Deprecated

(Since version 2.8.0) Use indexWhere(p) instead.

4. #### def findLastIndexOf(p: (A) ⇒ Boolean): Int

Returns index of the last element satisfying a predicate, or -1.

Returns index of the last element satisfying a predicate, or -1.

Definition Classes
SeqLike
Annotations
Deprecated

(Since version 2.8.0) use `lastIndexWhere` instead

5. #### def first: A

Definition Classes
IterableLike
Annotations
Deprecated

(Since version 2.8.0) use `head' instead`

6. #### def firstOption: Option[A]

`None` if iterable is empty.

`None` if iterable is empty.

Definition Classes
IterableLike
Annotations
Deprecated

(Since version 2.8.0) use `headOption' instead`

7. #### def projection: SeqView[A, Stream[A]]

returns a projection that can be used to call non-strict `filter`, `map`, and `flatMap` methods that build projections of the collection.

returns a projection that can be used to call non-strict `filter`, `map`, and `flatMap` methods that build projections of the collection.

Definition Classes
SeqLikeIterableLike
Annotations
Deprecated

(Since version 2.8.0) use `view' instead`

8. #### def reversedElements: Iterator[A]

Definition Classes
SeqLike
Annotations
Deprecated

(Since version 2.8.0) use `reverseIterator' instead`