How to Sort Multiple Vectors Based on the Values of a Single Vector?

Sorting Vectors Based on Values from a Different Vector

Consider a scenario where you have multiple vectors of the same length, and you want to sort one vector by a specified order while applying the same permutation to the other vectors. This poses the challenge of how to leverage this sorting pattern across multiple vectors.

Solution

To sort a vector by values from a different vector, you can employ a custom sorter and employ a vector that pairs each element's index with its corresponding value in the sorting vector.

typedef vector<int>::const_iterator myiter;

vector<pair<size_t, myiter>> order(Index.size());

size_t n = 0;
for (myiter it = Index.begin(); it != Index.end(); ++it, ++n)
    order[n] = make_pair(n, it);

struct ordering {
    bool operator ()(pair<size_t, myiter> const& a, pair<size_t, myiter> const& b) {
        return *(a.second) < *(b.second);
    }
};

sort(order.begin(), order.end(), ordering());

Once you have the sorted ordering, you can utilize this as a lookup table for the new index of each element in the other vectors.

template <typename T>
vector<T> sort_from_ref(
    vector<T> const& in,
    vector<pair<size_t, myiter>> const& reference
) {
    vector<T> ret(in.size());

    size_t const size = in.size();
    for (size_t i = 0; i < size; ++i)
        ret[i] = in[reference[i].first];

    return ret;
}

By applying this process, you can effectively sort the target vector and apply the same transformation to the corresponding elements in the other vectors.

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