org.apache.lucene.search.suggest.fst
Class FSTCompletionLookup

java.lang.Object
  org.apache.lucene.search.suggest.Lookup
      org.apache.lucene.search.suggest.fst.FSTCompletionLookup

public class FSTCompletionLookup
extends Lookup

An adapter from Lookup API to FSTCompletion.

This adapter differs from FSTCompletion in that it attempts to discretize any "weights" as passed from in TermFreqIterator.weight() to match the number of buckets. For the rationale for bucketing, see FSTCompletion.

Note:Discretization requires an additional sorting pass.

The range of weights for bucketing/ discretization is determined by sorting the input by weight and then dividing into equal ranges. Then, scores within each range are assigned to that bucket.

Note that this means that even large differences in weights may be lost during automaton construction, but the overall distinction between "classes" of weights will be preserved regardless of the distribution of weights.

For fine-grained control over which weights are assigned to which buckets, use FSTCompletion directly or TSTLookup, for example.

See Also:

FSTCompletion

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.search.suggest.Lookup

Lookup.LookupPriorityQueue, Lookup.LookupResult

Field Summary

Fields inherited from class org.apache.lucene.search.suggest.Lookup

CHARSEQUENCE_COMPARATOR

Constructor Summary

FSTCompletionLookup()
This constructor prepares for creating a suggested FST using the build(TermFreqIterator) method.

FSTCompletionLookup(FSTCompletion completion, boolean exactMatchFirst)
This constructor takes a pre-built automaton.

FSTCompletionLookup(int buckets, boolean exactMatchFirst)
This constructor prepares for creating a suggested FST using the build(TermFreqIterator) method.

Method Summary

void	build(TermFreqIterator tfit) Builds up a new internal Lookup representation based on the given TermFreqIterator.
Object	get(CharSequence key)
boolean	load(InputStream input) Discard current lookup data and load it from a previously saved copy.
List<Lookup.LookupResult>	lookup(CharSequence key, boolean higherWeightsFirst, int num) Look up a key and return possible completion for this key.
boolean	store(OutputStream output) Persist the constructed lookup data to a directory.

Methods inherited from class org.apache.lucene.search.suggest.Lookup

build

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FSTCompletionLookup

public FSTCompletionLookup()

This constructor prepares for creating a suggested FST using the build(TermFreqIterator) method. The number of weight discretization buckets is set to FSTCompletion.DEFAULT_BUCKETS and exact matches are promoted to the top of the suggestions list.

FSTCompletionLookup

public FSTCompletionLookup(int buckets,
                           boolean exactMatchFirst)

This constructor prepares for creating a suggested FST using the build(TermFreqIterator) method.

Parameters:

buckets - The number of weight discretization buckets (see FSTCompletion for details).

exactMatchFirst - If true exact matches are promoted to the top of the suggestions list. Otherwise they appear in the order of discretized weight and alphabetical within the bucket.

FSTCompletionLookup

public FSTCompletionLookup(FSTCompletion completion,
                           boolean exactMatchFirst)

This constructor takes a pre-built automaton.

Parameters:

completion - An instance of FSTCompletion.

exactMatchFirst - If true exact matches are promoted to the top of the suggestions list. Otherwise they appear in the order of discretized weight and alphabetical within the bucket.

Method Detail

build

public void build(TermFreqIterator tfit)
           throws IOException

Builds up a new internal Lookup representation based on the given TermFreqIterator. The implementation might re-sort the data internally.

Specified by:

build in class Lookup

Throws:

IOException

lookup

public List<Lookup.LookupResult> lookup(CharSequence key,
                                        boolean higherWeightsFirst,
                                        int num)

Description copied from class: Lookup

Look up a key and return possible completion for this key.

Specified by:

lookup in class Lookup

Parameters:

key - lookup key. Depending on the implementation this may be a prefix, misspelling, or even infix.

higherWeightsFirst - return only more popular results

num - maximum number of results to return

Returns:

a list of possible completions, with their relative weight (e.g. popularity)

get

public Object get(CharSequence key)

store

public boolean store(OutputStream output)
              throws IOException

Description copied from class: Lookup

Persist the constructed lookup data to a directory. Optional operation.

Specified by:

store in class Lookup

Parameters:

output - OutputStream to write the data to.

Returns:

true if successful, false if unsuccessful or not supported.

Throws:

IOException - when fatal IO error occurs.

load

public boolean load(InputStream input)
             throws IOException

Description copied from class: Lookup

Discard current lookup data and load it from a previously saved copy. Optional operation.

Specified by:

load in class Lookup

Parameters:

input - the InputStream to load the lookup data.

Returns:

true if completed successfully, false if unsuccessful or not supported.

Throws:

IOException - when fatal IO error occurs.