boost zip_iterator and std::sort

Question

I have two arrays values and keys both of the same length. I want to sort-by-key the values array using the keys array a

Answer 1

A very good discussion of this problem can be found here: https://web.archive.org/web/20120422174751/http://www.stanford.edu/~dgleich/notebook/2006/03/sorting_two_arrays_simultaneou.html

Here's a possible duplicate of this question: Sorting zipped (locked) containers in C++ using boost or the STL

The approach in the link above uses std::sort, and no extra space. It doesn't employ boost::zip_iterator, just boost tuples and the boost iterator facade. Std::tuples should also work if you have an up to date compiler.

If you are happy to have one extra vector (of size_t elements), then the following approach will work in ~ o(n log n) time average case. It's fairly simple, but there will be better approaches out there if you search for them.

#include 
#include 
#include 
#include 

using namespace std;

template 
void sortByPerm(vector& list1, vector& list2) {
  const auto len = list1.size();
  if (!len || len != list2.size()) throw;

  // create permutation vector
  vector perms;
  for (size_t i = 0; i < len; i++) perms.push_back(i);
  sort(perms.begin(), perms.end(), [&](T1 a, T1 b){ return list1[a] < list1[b]; });

  // order input vectors by permutation
  for (size_t i = 0; i < len - 1; i++) {
    swap(list1[i], list1[perms[i]]);
    swap(list2[i], list2[perms[i]]);

    // adjust permutation vector if required
    if (i < perms[i]) {
      auto d = distance(perms.begin(), find(perms.begin() + i, perms.end(), i));
      swap(perms[i], perms[d]);
    }
  }
}

int main() {
  vector ints = {32, 12, 40, 8, 9, 15};
  vector doubles = {55.1, 33.3, 66.1, 11.1, 22.1, 44.1};

  sortByPerm(ints, doubles);   

  copy(ints.begin(), ints.end(), ostream_iterator(cout, " ")); cout << endl;
  copy(doubles.begin(), doubles.end(), ostream_iterator(cout, " ")); cout << endl;
}