C++ sorting and keeping track of indexes

Question

Using C++, and hopefully the standard library, I want to sort a sequence of samples in ascending order, but I also want to remember the original indexes of the new samples.<

Answer 1

There is another way to solve this, using a map:

vector v = {...}; // input data
map m; // mapping from value to its index
for (auto it = v.begin(); it != v.end(); ++it)
    m[*it] = it - v.begin();

This will eradicate non-unique elements though. If that's not acceptable, use a multimap:

vector v = {...}; // input data
multimap m; // mapping from value to its index
for (auto it = v.begin(); it != v.end(); ++it)
    m.insert(make_pair(*it, it - v.begin()));

In order to output the indices, iterate over the map or multimap:

for (auto it = m.begin(); it != m.end(); ++it)
    cout << it->second << endl;