Boost Multiarray Dimensions

Question

I have a Boost multiarray whose dimensions are set at run-time based on input from the user.

I'd now like to iterate over that array via x,y,z components.

If this were a std::vector, I would use:

for(int i=0;i<v.size();i++){

Or perhaps some kind of iterator.

How do I get numeric values of the multiarray's dimensions?

How do I iterate over the multiarray?

score 16 · Accepted Answer · answered Sep 15 '13 at 11:32

You could use shape() for a less convoluted way:

#include <iostream>
#include <string>
#include <boost/multi_array.hpp>

int main() {
    boost::multi_array<std::string, 2> a(boost::extents[3][5]);
    for(size_t x = 0; x < a.shape()[0]; x++) {
        for(size_t y = 0; y < a.shape()[1]; y++) {
            std::ostringstream sstr;
            sstr << "[" << x << ", " << y << "]";
            a[x][y] = sstr.str();
        }
    }
    for(size_t x = 0; x < a.shape()[0]; x++) {
        for(size_t y = 0; y < a.shape()[1]; y++) {
            std::cout << a[x][y] << "\n";
        }
    }
    return 0;
}

(See it in action on coliru)

score 4 · Answer 2 · answered Feb 16 '12 at 16:29

#include "boost/multi_array.hpp"
#include <iostream>
#include <algorithm>
#include <iterator>

int main () {
    typedef boost::multi_array_types::index_range range;
    typedef boost::multi_array<char, 2> Array2d;
    Array2d a(boost::extents[8][24]);

    //to view the two-dimensional array as a one-dimensional one can use multi_array_ref?
    boost::multi_array_ref<char, 1> a_ref(a.data(), boost::extents[a.num_elements()]);
    std::fill(a_ref.begin(), a_ref.end(), '-');

    //to apply algorithm to one row or column, can use array_view
    //especially useful for traversing it vertically?
    //e.g:
    Array2d::array_view<1>::type views[4] = {
        a[boost::indices[range()][0]], //left column
        a[boost::indices[range()][a[0].size() - 1]], //right column
        a[boost::indices[0][range()]], //top row
        a[boost::indices[a.size()-1][range()]] //bottom row
    };
    for (unsigned i = 0; i != sizeof(views)/sizeof(views[0]); ++i) {
        std::fill ( views[i].begin(), views[i].end(), 'X' );
    }

    //output
    for (unsigned i = 0; i != a.size(); ++i) {
        std::copy(a[i].begin(), a[i].end(), std::ostream_iterator<char>(std::cout, ""));
        std::cout << '\n';
    }
}

source: http://cboard.cprogramming.com/cplusplus-programming/112584-boost-multiarray.html

Thanks. This looks so convoluted that I looked into matters, and I'm going to try the boost uBLAS matrix instead. — Richard, Feb 16 '12 at 17:28
I had some "fun" with uBLAS and shared pointers once, can't remember the details. What about looking at the tuple type in C++11? — Damian, Feb 16 '12 at 22:07

Boost Multiarray Dimensions

2 Answers2