std::slice

 

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valarray::valarray valarray::~valarray valarray::operator= valarray::operator[] valarray::swap valarray::size valarray::resize valarray::sum valarray::min valarray::max valarray::shift valarray::cshift valarray::apply	valarray::operator+ valarray::operator- valarray::operator~ valarray::operator! valarray::operator*= valarray::operator/= valarray::operator%= valarray::operator+= valarray::operator-= valarray::operator^= valarray::operator&= valarray::operator|= valarray::operator<<= valarray::operator>>=
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swap (C++11) begin (C++11) end (C++11) abs exp log log10 pow sqrt sin cos tan asin acos atan atan2 sinh cosh tanh	operator* operator/ operator% operator+ operator- operator^ operator& operator| operator<< operator>> operator&& operator operator== operator!= operator< operator> operator<= operator>=
Helper classes
slice_array gslice_array indirect_array	slice gslice mask_array

 

Defined in header <valarray>
class slice;

std::slice is the selector class that identifies a subset of std::valarray similar to BLAS slice. An object of type std::slice holds three values: the starting index, the stride, and the total number of values in the subset. Objects of type std::slice can be used as indexes with valarray's operator[].

Member functions

(constructor)	constructs a slice (public member function)
start	accesses the start of the slice (public member function)
size	accesses the size of the slice (public member function)
stride	accesses the stride of the slice (public member function)

Example

Barebones valarray-backed Matrix class with a trace calculating function.

#include <iostream>
#include <valarray>
class Matrix {
    std::valarray<int> data;
    int dim;
 public:
    Matrix(int r, int c) : data(r*c), dim(c) {}
    int& operator()(int r, int c) {return data[r*dim + c];}
    int trace() const {
        return data[std::slice(0, dim, dim+1)].sum();
    }
};
int main()
{
    Matrix m(3,3);
    int n = 0;
    for(int r=0; r<3; ++r)
       for(int c=0; c<3; ++c)
           m(r, c) = ++n;
    std::cout << "Trace of the matrix (1,2,3) (4,5,6) (7,8,9) is " << m.trace() << '\n';
}

Output:

Trace of the matrix (1,2,3) (4,5,6) (7,8,9) is 15

See also

operator[]	get/set valarray element, slice, or mask (public member function)
gslice	generalized slice of a valarray: starting index, set of lengths, set of strides (class)
slice_array	proxy to a subset of a valarray after applying a slice (class template)