std::gslice_array
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std::valarray
std::gslice_array
Member functions
Defined in header
<valarray>
template< class T >
class gslice_array;
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.
[edit] Member types
Type
Definition
value_type
T
[edit] Member functions
performs arithmetic operation on the array referred by generic slice.
(public member function) [edit]
(public member function) [edit]
[edit] 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