std::gslice_array

 

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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
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std::gslice_array

Member functions

gslice_array::gslice_array

gslice_array::~gslice_array

gslice_array::operator=

gslice_array::operator+=gslice_array::operator-=gslice_array::operator*=gslice_array::operator/=gslice_array::operator%=gslice_array::operator&=gslice_array::operator|=gslice_array::operator^=gslice_array::operator<<=gslice_array::operator>>=

 

Defined in header <valarray>
template< class T > class gslice_array;

std::gslice_array is a helper template used by the valarray subscript operator with std::gslice argument. It has reference semantics to a subset of the array specified by the std::gslice object.

Member types

Type	Definition
value_type	T

Member functions

(constructor)	constructs a gslice_array (public member function)
(destructor)	destroys a gslice_array (public member function)
operator=	assigns contents (public member function)
operator+=operator-=operator*=operator/=operator%=operator&=operator|=operator^=operator<<=operator>>=	performs arithmetic operation on the array referred by generic slice. (public member function)

Example

Run this code

#include <cassert>
#include <cstddef>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <valarray>
 
int main()
{
    std::valarray<int> data(32);
    std::iota(std::begin(data), std::end(data), 0);
 
    const std::size_t offset = 1, z = 2, y = 3, x = 4;
    const std::valarray<std::size_t> sizes{z, y, x};
    const std::valarray<std::size_t> strides{15, 5, 1};
    const std::gslice gslice = std::gslice(offset, sizes, strides);
    / Indices are generated according to the formula:
    / index[k] = offset + [0,1,2)*15 + [0,1,2,3)*5 + [0,1,2,3,4)*1
    /          = offset + inner_product(sizes[k], strides);
    / where sizes[k] = {[0,z), [0,y), [0,x)}, while the rightmost index (x)
    / runs fastest. As a result we have following set of indices:
    /  index[0]  = 1 + 0*15 + 0*5 + 0*1 = 1
    /  index[1]  = 1 + 0*15 + 0*5 + 1*1 = 2
    /  index[2]  = 1 + 0*15 + 0*5 + 2*1 = 3
    /  index[3]  = 1 + 0*15 + 0*5 + 3*1 = 4
    /  index[4]  = 1 + 0*15 + 1*5 + 0*1 = 6
    /  index[5]  = 1 + 0*15 + 1*5 + 1*1 = 7
    /  index[6]  = 1 + 0*15 + 1*5 + 2*1 = 8
    /  index[7]  = 1 + 0*15 + 1*5 + 3*1 = 9
    /  ...
    /  index[22] = 1 + 1*15 + 2*5 + 2*1 = 28
    /  index[23] = 1 + 1*15 + 2*5 + 3*1 = 29
 
    const std::valarray<int> indices = data[gslice];
    for (unsigned i = 0; i != indices.size(); ++i)
        std::cout << std::setfill('0') << std::setw(2) << indices[i] << ' ';
    std::cout << "\nTotal indices: " << indices.size() << '\n';
    assert(indices.size() == x * y * z);
 
    data = 0;
    std::gslice_array<int> gslice_array = data[gslice];
    gslice_array = 1;
    / Cells that correspond to generated indices = '1', skipped cells = '0'.
    for (auto i : data)
        std::cout << i << ' ';
    std::cout << "\nSum of ones = " << data.sum() << '\n';
}

Output:

01 02 03 04 06 07 08 09 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29 
Total indices: 24
0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 0 
Sum of ones = 24

See also

slice_array	proxy to a subset of a valarray after applying a slice (class template)
mdspan (C++23)	a multi-dimensional non-owning array view (class template)

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