Question

Given a multimap<A,B> M what’s a neat way to create a vector<B> of all values in M with a specific key.

e.g given a multimap how can I get a vector of all strings mapped to the value 123?

An answer is easy, looping from lower->upper bound, but is there a neat loop-free method?

Answer 1

Here’s the way to do it STL style :

// The following define is needed for select2nd with DinkumWare STL under VC++
#define _HAS_TRADITIONAL_STL 1

#include <algorithm>
#include <vector>
#include <map>
#include <string>
#include <functional>
#include <map>
#include <iterator>
#include <iostream>

using namespace std;

void main()
{
    typedef multimap<string, int> MapType;
    MapType m;
    vector<int> v;

    // Test data
    for(int i = 0; i < 10; ++i)
    {
        m.insert(make_pair("123", i * 2));
        m.insert(make_pair("12", i));
    }

    MapType::iterator i = m.lower_bound("123");
    MapType::iterator j = m.upper_bound("123");

    transform(i, j, back_inserter(v), select2nd<MapType::value_type>());

    copy(v.begin(), v.end(),  ostream_iterator<int>(cout, ","));

}