Obtaining list of keys and values from unordered_map

Question

What is the most efficient way of obtaining lists (as a vector) of the keys and values from an unordered_map?

For concreteness, suppose the

Answer 1

Okay, here you go:

std::vector keys;
keys.reserve(map.size());
std::vector vals;
vals.reserve(map.size());

for(auto kv : map) {
    keys.push_back(kv.first);
    vals.push_back(kv.second);  
} 

Efficiency can probably be improved, but there it is. You're operating on two containers though, so there's not really any STL magic that can hide that fact.

As Louis said, this will work for any of the STL map or set containers.