sortIndices.h

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//
// Created by Nikhil Chandra Admal on 9/30/22.
// https://stackoverflow.com/questions/1577475/c-sorting-and-keeping-track-of-indexes
 
#ifndef OILAB_SORTINDICES_H
#define OILAB_SORTINDICES_H
 
#include <iostream>
#include <vector>
#include <numeric>      // std::iota
#include <algorithm>    // std::sort, std::stable_sort
 
using namespace std;
 
namespace oILAB {
template <typename ArrayType> vector<size_t> sortIndices(const ArrayType &v) {
 
  // initialize original index locations
  vector<size_t> idx(v.size());
  iota(idx.begin(), idx.end(), 0);
 
  // sort indexes based on comparing values in v
  // using std::stable_sort instead of std::sort
  // to avoid unnecessary index re-orderings
  // when v contains elements of equal values
  stable_sort(idx.begin(), idx.end(),
              [&v](size_t i1, size_t i2) { return abs(v(i1)) > abs(v(i2)); });
 
  return idx;
    }
    } // namespace oILAB
#endif //OILAB_SORTINDICES_H