slice_array.cpp

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#include <iostream>    // for cout, endl
#include <valarray.h>  // Includes valarray and provides stream inserter.
#include <examples.h>  // Generic header for all examples.
 
typedef std::valarray<int> valarray_t;
 
int main(void) {
 
    valarray_t::value_type ibuf[9] = {0,1,2,3,4,5,6,7,8};
 
    // Create a valarray initialized to the sequence of integers above.
    valarray_t vi (ibuf,9);
 
    std::cout << "original valarray vi\n\n" << vi << "\n\n";
 
    // Display a slice of the valarray.
    std::cout << "vi[slice(0,3,3)]\n\n"  << vi[std::slice(0,3,3)] << "\n\n";
 
    // Unfortunately, slice_arrays were not designed to be easily combined.
    // An explicit conversion to valarray is required, leaving us with
    // this awkward casting syntax.
    vi[std::slice (0,3,3)] = static_cast<valarray_t>(vi[std::slice (1,3,3)]) +
                             static_cast<valarray_t>(vi[std::slice (2,3,3)]);
 
    // The operation above uses slices ([0-2],3,3) to treat our valarray
    // as a 3-dimensional array:
    //
    //  0 1 2                 3 = 1 + 2
    //  3 4 5                 9 = 4 + 5
    //  6 7 8                15 = 7 + 8
    //  | | |                 |   |   |
    //  | | --slice(2,3,3)    |   |   -slice_array for arithmetic operand.
    //  | ----slice(1,3,3)    |   -----slice_array for arithmetic operand.
    //  ------slice(0,3,3)    ----slice_array assignment refers to valarray.
 
    std::cout << "vi[slice(0,3,3)] = vi[slice(1,3,3)] + vi[slice(2,3,3)]\n\n"
              << vi << std::endl;
 
    return 0;
}