std::slice

 

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std::valarray

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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(std::valarray) (C++11) begin(std::valarray) (C++11)   end(std::valarray) (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>=
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slice_array gslice_array indirect_array	slice gslice mask_array
Deduction guides (C++17)

 

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.

Run this code

#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

Template:cpp/numeric/valarray/dcl list operator atTemplate:cpp/numeric/valarray/dcl list gsliceTemplate:cpp/numeric/valarray/dcl list slice array