Re: Initialize a std::set with keys from a std::map
brzrkr0@gmail.com wrote:
A portion of my program needs to initialize a std::set<int> to have
all the keys in a std::map<int, double>. The code I've pasted below
works, but I'm wondering if there's a more elegant way to do it (an
STL algorithm, maybe?). I'm a bit of an STL noob, so any advice
people can give would be greatly appreciated.
transform( map->begin(), map->end(), inserter( v, v.begin() ),
select1st<intDoubleMap::value_type>() );
Note, "select1st" is part of the STL, but not part of the standard
library. It's easy to implement though and is generally useful:
template <typename Pair>
struct select1st : unary_function<Pair, typename Pair::first_type>
{
const typename Pair::first_type& operator()(const Pair& x) const {
return x.first;
}
};
Or you can use the boost lambda library:
transform( map->begin(), map->end(), inserter( v, v.begin() ),
bind(&intDoubleMap::value_type::first, _1 ) );
typedef std::map<int, double> intDoubleMap;
typedef std::set<int> intSet;
intSet v;
// map is an intDoubleMap* and has been initialized with some values
for (intDoubleMap::const_iterator it = map->begin();
it != map->end();
it++) {
int i = it->first;
v.insert(i);
}
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