Sorting two corresponding arrays

Question

I have this code here that has two arrays. It sorts arr[], so that the highest value will be in index 0. Now the second array arr1[] contains strings, I'd like the code to apply whatever changes where made to arr[] to arr1[]. So that arr[0] would return 6, while arr1[0] would return the string "d1". Notice how "d1" was at the same index as 6? After sorting I'd like the same values to still have their string counterparts.

How would I go about doing this?

#include <iostream> #include <iomanip> #include <algorithm> #include <functional> using namespace std;  int main() {   int arr[ 5 ] = { 4, 1, 3, 6, 2 };     string arr1[ 5 ] = { "a1", "b1", "c1", "d1", "e1" };    std::sort( arr, arr + 5, std::greater< int >() );   cout << arr[0] << arr1[0] << endl;    system("pause"); } 

Answer 1

Rather than sort the arrays, sort the indices. I.e., you have

int arr[5]={4,1,3,6,2} string arr1[5]={"a1","b1","c1","d1","e1"}; 

and you make

int indices[5]={0,1,2,3,4}; 

now you make a sort indices comparator that looks like this (just and idea, you'll probably have to fix it a little)

class sort_indices {    private:      int* mparr;    public:      sort_indices(int* parr) : mparr(parr) {}      bool operator()(int i, int j) const { return mparr[i]<mparr[j]; } } 

now you can use the stl sort

std::sort(indices, indices+5, sort_indices(arr)); 

when you're done, the indices array will be such that arr[indices[0]] is the first element. and likewise arr1[indices[0]] is the corresponding pair.

This is also a very useful trick when you're trying to sort a large data object, you don't need to move the data around at every swap, just the indices.