multisort.h

#ifndef MULTISORT
#define MULTISORT

#include <algorithm> // stable_sort
#include <array> // array
#include <numeric> // iota
#include <vector> // vector

namespace Multisort {

    template<typename T, size_t N>
    bool less(const std::array<T, N>& a, const std::array<T, N>& b)
    {
        for (unsigned int i = 0; i < N; i++) {
            if (a[i] < b[i])
                return true;
            if (a[i] > b[i])
                return false;
        }
        return false; // all equal
    }

    template<typename T, size_t N>
    void sort(std::vector<std::array<T, N> > v, int* index)
    {
        int n = v.size();
        std::iota(index, index + n, 0);
        std::stable_sort
            (index, index + n, [&v](int i, int j){return less(v[i], v[j]); });
    }

} // namespace Multisort

#endif