How to sort and rank a vector in C++ (without using C++11)

Question

I am trying to construct a function take takes a vector, ranks it, sorts it and outputs the sorted and ranked vector with the original positioning of the values. For example: I

Answer 1

Your problem is a misconception on rankings. Array indices are of size_t not float, so you'll need to return a vector not a vector.

That said your sort is O(n²). If you're willing to use more memory we can get that time down to O(n log(n)):

vector rankSort(const float* v_temp, const size_t size) {
    vector > v_sort(size);

    for (size_t i = 0U; i < size; ++i) {
        v_sort[i] = make_pair(v_temp[i], i);
    }

    sort(v_sort.begin(), v_sort.end());

    pair rank;
    vector result(size);

    for (size_t i = 0U; i < size; ++i) {
        if (v_sort[i].first != rank.first) {
            rank = make_pair(v_sort[i].first, i);
        }
        result[v_sort[i].second] = rank.second;
    }
    return result;
}

Live Example

EDIT:

Yeah this actually gets a little simpler when taking a vector instead of a float[]:

vector rankSort(const vector& v_temp) {
    vector > v_sort(v_temp.size());

    for (size_t i = 0U; i < v_sort.size(); ++i) {
        v_sort[i] = make_pair(v_temp[i], i);
    }

    sort(v_sort.begin(), v_sort.end());

    pair rank;
    vector result(v_temp.size());

    for (size_t i = 0U; i < v_sort.size(); ++i) {
        if (v_sort[i].first != rank.first) {
            rank = make_pair(v_sort[i].first, i);
        }
        result[v_sort[i].second] = rank.second;
    }
    return result;
}

Live Example