vector to map

Question

i have an vector > v and want to make a map from it i came up with 3 variants: std::transform(v.begin(),v.end(), std::inserter(map,map.begin()),[](std::tuple t){ return std::make_pair(std::get<0>(t),std::get<1>(t)); }); std::for_each(v.begin(), v.end(), [](std::tuple t){ map.insert(std::make_pair(std::get<0>(t),std::get<1>(t))); }); for (auto t : v) { map.insert(std::make_pair(std::get<0>(t),std::get<1>(t))); } is shorter is better the way to go here? could one simplify the tuple=>pair conversion? thanks

Anton Golov · Answer

I would use the last as the simplest, yes. I'd probably write a pair_from_tuple helper function to not have to write out the std::get explicitly.

The first and second both require you to write out the tuple type. This will change soon, but not everyone will immediately have C++14. Also, they're easier to get wrong; I think you mean to specify capture-by-reference in example 2, for example.

With pair_from_tuple, I suppose

using std::begin;
using std::end;
std::transform(begin(v), end(v), std::inserter{map, map.begin()}, pair_from_tuple<int, char>);

would be okay (you can avoid the <int, char> by making pair_from_tuple a functor). Still less nice than

for (auto const& e : v)
    map.insert(pair_from_tuple(e));

, though.

vector<tuple > to map

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