C++, Sort One Vector Based On Another One

Question

The best example I've got is that I want to sort Names based on their Score.

vector <string> Names {"Karl", "Martin", "Paul", "Jennie"}; vector <int> Score{45, 5, 14, 24}; 

So if I sort the score to {5, 14, 24, 45}, the names should also be sorted based on their score.

Answer 1

An alternative to consolidating the names and scores into a single structure is to create an index list and sort that:

 std::vector<int> indices(Names.size());  std::iota(indices.begin(), indices.end(), 0);  std::sort(indices.begin(), indices.end(),            [&](int A, int B) -> bool {                 return Score[A] < Score[B];             }); 

Now indices can be used to index Names and Scores in the desired sorted order.

Answer 2

As already suggested in other answers: Combining the name and the score of each individual is likely the simplest solution.

Generically, this can be achieved with what is sometimes referred to as a "zip" operation: Combining two vectors into a vector of pairs - along with a corresponding "unzip".

Implemented generically, this may look as follows:

#include <vector> #include <string> #include <algorithm> #include <iostream> #include <iterator>  // Fill the zipped vector with pairs consisting of the // corresponding elements of a and b. (This assumes  // that the vectors have equal length) template <typename A, typename B> void zip(     const std::vector<A> &a,      const std::vector<B> &b,      std::vector<std::pair<A,B>> &zipped) {     for(size_t i=0; i<a.size(); ++i)     {         zipped.push_back(std::make_pair(a[i], b[i]));     } }  // Write the first and second element of the pairs in  // the given zipped vector into a and b. (This assumes  // that the vectors have equal length) template <typename A, typename B> void unzip(     const std::vector<std::pair<A, B>> &zipped,      std::vector<A> &a,      std::vector<B> &b) {     for(size_t i=0; i<a.size(); i++)     {         a[i] = zipped[i].first;         b[i] = zipped[i].second;     } }   int main(int argc, char* argv[]) {     std::vector<std::string> names {"Karl", "Martin", "Paul", "Jennie"};     std::vector<int> score {45, 5, 14, 24};      // Zip the vectors together     std::vector<std::pair<std::string,int>> zipped;     zip(names, score, zipped);      // Sort the vector of pairs     std::sort(std::begin(zipped), std::end(zipped),          [&](const auto& a, const auto& b)         {             return a.second > b.second;         });      // Write the sorted pairs back to the original vectors     unzip(zipped, names, score);      for(size_t i=0; i<names.size(); i++)     {         std::cout << names[i] << " : " << score[i] << std::endl;     }     return 0; }