How Can I Sort Data in C While Tracking Original Indices?

Sorting with Index Tracking in C

Sorting data while preserving original indexes is a common task in data analysis and manipulation. In C , achieving this requires some thoughtful programming techniques.

To sort a sequence of samples in ascending order while tracking their original indexes, one can utilize lambda expressions and the standard library. The sort_indexes function below demonstrates this approach:

template <typename T>
vector<size_t> sort_indexes(const vector<T> &v) {
  // Initialize original index locations
  vector<size_t> idx(v.size());
  iota(idx.begin(), idx.end(), 0);

  // Sort indexes based on values in v using std::stable_sort to maintain original order for equal values
  stable_sort(idx.begin(), idx.end(),
    [&v](size_t i1, size_t i2) { return v[i1] < v[i2]; });

  return idx;
}

This function returns an index vector that can be used in subsequent iterations:

for (auto i : sort_indexes(v)) {
  cout << v[i] << endl;
}

Customizations can be made to provide a sort function, comparator, or automatic reordering of the original vector within the sort_indexes function.

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