std::gslice | Valarray Generalized Slicing Selector

std::gslice is a class defined in the <valarray> header of the C++ Standard Library that enables the selection of a sub-section of a std::valarray data structure in a flexible way.

Syntax

The syntax for std::gslice is as follows:

valarray<T> val(gslice spec);

where spec is a std::gslice object that specifies the starting indices, the size, and the strides of the sub-section to be selected.

How it Works

std::valarray is a container data structure that holds a sequence of elements of type T. It is particularly useful for performing mathematical and statistical operations on arrays of data.

The std::gslice object represents a generalized slice of the std::valarray data structure. It is specified by four parameters:

• start: an array of indices, one for each dimension of the std::valarray, indicating the starting position of the sub-section to be selected along each dimension.
• size: an array of integers, one for each dimension of the std::valarray, indicating the size of the sub-section to be selected along each dimension.
• stride: an array of integers, one for each dimension of the std::valarray, indicating the number of elements between consecutive elements along each dimension of the sub-section.
• d: the number of dimensions of the std::valarray.

The parameter start is of type std::slice, the parameter size is of type std::gslice, and the parameter stride is of type std::gslice.

Example

Here's an example of how to use std::gslice to select a sub-section of a std::valarray object:

#include <iostream>
#include <valarray>

int main() {
    std::valarray<int> a{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    std::gslice spec{std::slice{1, 3, 2}, {2, 2}, {3, 1}};

    std::valarray<int> b = a[spec];
    std::cout << "b: ";
    for (int i : b) std::cout << i << " ";
    std::cout << std::endl;

    return 0;
}

In this example, we define a std::valarray object a with 10 elements. We then define a std::gslice object spec that selects a sub-section of a starting at index 1 and skipping every other element, with a size of 2x2. We then use the [] operator to apply the std::gslice object to a, which creates a new std::valarray object b containing the selected sub-section. Finally, we output the contents of b to the console.

The output of this program should be:

b: 3 4 7 8

Conclusion

std::gslice is a powerful and flexible tool for selecting sub-sections of std::valarray objects. By specifying the starting indices, the size, and the strides of the sub-section, you can select any portion of the array that you need. This can be useful for a wide range of applications, from data analysis to numerical simulation.