Re: copy from keys from multimap into the vector
Salt_Peter wrote:
On Oct 29, 2:33?pm, puzzlecracker <ironsel2...@gmail.com> wrote:
I am using while loop for that but I am sure you can do it quicker and
more syntactically clear with copy function.
Here is what I do and would like to if someone has a cleaner solution:
vector<string> vec;
multimap<stirng, int> myMap
// populate myMap
multimap<string, int >::iterator iter = myMap.begin();
while(iter != myMap.end())
{
vec.push_back(iter->first)
}
You could use std::transform with std::back_inserter to load vector
and a functor to extract the std::string from multimap's value_type.
#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iterator>
template< typename P >
struct extract_first
{
const typename P::first_type&
operator()(const P& p) const
{
return p.first;
}
};
int main()
{
std::vector< std::string > vec;
std::multimap< std::string, int > mm;
// populate mm
typedef std::multimap< std::string, int >::value_type VType;
std::transform( mm.begin(),
mm.end(),
std::back_inserter(vec),
extract_first< VType >() );
}
Alternatively, one can put the template inside:
// same headers
struct extract_first {
template< typename P >
typename P::first_type const &
operator()(const P& p) const {
return p.first;
}
};
int main() {
std::vector< std::string > vec;
std::multimap< std::string, int > mm;
// populate mm
std::transform( mm.begin(),
mm.end(),
std::back_inserter(vec),
extract_first() );
}
This makes extract_first oblivious to the type actually being used. I am not
sure, which is better. Any thoughts?
Best
Kai-Uwe Bux