Convert multimap<Key,Value> to vector<vector<Value>> - c++

Question

I need to convert an std::unordered_multimap<Key,T> to an std::vector<std::vector<T>>. I need to do this because my program will need to sort all the data, and maps can't be sorted. An example:
// Map:
{ "A", 1 },
{ "A", 3 },
{ "A", 2 },
{ "B", 5 },
{ "B", 2 },
// Map converted to vector<vector<Value>>:
{ 1, 3, 2 },
{ 5, 2 }
Right now I have this code which works. But I'm wondering if it's the best way to do it.
#include <unordered_map>
#include <iostream>
#include <string>
#include <vector>
int main()
{
typedef std::string Key_t;
typedef int Value_t;
typedef std::unordered_multimap<Key_t, Value_t> Map_t;
const Map_t map = {
{ "A", 1 },
{ "A", 3 },
{ "A", 2 },
{ "B", 5 },
{ "B", 2 },
};
std::vector< std::vector< Value_t > > output;
for ( Map_t::const_iterator it = map.cbegin(); it != map.cend(); )
{
std::vector< Value_t > temp;
const Map_t::const_iterator end = map.upper_bound( it->first );
for ( ; it != end; ++it )
temp.push_back( it->second );
output.push_back( temp );
}
// Print the result
for ( const std::vector< Value_t >& values : output )
{
for ( const Value_t& value : values )
std::cout << value << " ";
std::cout << std::endl;
}
}
Output:
1 3 2
5 2
So, now I'm wondering if there's a faster/better way.

Answer 1

here's my attempt.
proof is here: http://goo.gl/JVpHw9
#include <unordered_map>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
int main()
{
typedef std::string Key_t;
typedef int Value_t;
typedef std::unordered_multimap<Key_t, Value_t> Map_t;
const Map_t map = {
{ "A", 1 },
{ "A", 3 },
{ "A", 2 },
{ "B", 5 },
{ "B", 2 },
};
std::vector< std::vector< Value_t > > output;
for (auto it = map.begin(); it != map.end(); )
{
auto er = map.equal_range(it->first);
auto tmp = std::vector< Value_t >{};
for( ; it != er.second ; ++it) {
tmp.push_back(it->second);
};
output.push_back(std::move(tmp));
}
// Print the result
for ( const std::vector< Value_t >& values : output )
{
for ( const Value_t& value : values )
std::cout << value << " ";
std::cout << std::endl;
}
}

Answer 2

The usual multimap iteration should work here:
std::vector<std::vector<T>> out;
for (auto it1 = m.begin(), it2 = it1, end = m.end(); it1 != end; it1 = it2)
{
out.emplace_back();
for ( ; it1->first == it2->first; ++it2)
{
out.back().push_back(it2->second);
}
}

Answer 3

Following works for me:
#include <vector>
#include <iostream>
#include <algorithm>
#include <unordered_map>
int main () {
std::unordered_multimap<std::string, int> map;
map = {
{ "A", 1 },
{ "A", 3 },
{ "A", 2 },
{ "B", 5 },
{ "B", 2 },
};
std::vector<int> values;
std::transform(map.begin(), map.end(),
std::back_inserter(values),
[](std::pair<std::string, int> element) {
return element.second;
});
for (auto const& value : values) {
std::cout << value << std::endl;
}
return 0;
}