Remove duplicate key in a multimap - c++

Question

I have a multimap:
std::multimap < string, string >::iterator iter_map;
multimap < string, set<string> > my.map;
Typical output and data structure:
key - value
bird - air
bird - earth
fish - water
lion - earth
lion - water
I would like change the data structure (no only print to) such that that the new data
would be:
bird - air, earth
fish - water
lion - earth, water
In other way, how to eliminate the duplicate keys?
I did this:
int size_mmap = namesMultiMap1.size();
pair<multimap<string,string>::iterator,multimap<string,string>::iterator> ret;
for (int i = 0; i < 1; i++){
cout << " xxx "<< " =>";
ret = namesMultiMap1.equal_range("xxx");
for (nameItr1=ret.first; nameItr1!=ret.second; ++nameItr1)
cout << " " << (*nameItr1).second;
}
In this way I print the values associeted at a key xxx but I print a element at once.
I would like to print all keys and values. I need automated this because the map is big.
If I iterate using a iterator for namesMultiMap1 a print the repeat keys.

Answer 1

Ok, this can be done like follows. Notice, that the type of the result is map<string, set<string> >, not multimap < string, set<string> > as you wanted, cause you don't want duplicated keys in it, so map makes more sense.
#include <map>
#include <set>
#include <string>
#include <iostream>
#include <iterator>
using namespace std;
typedef multimap<string,string> mm;
typedef map<string, set<string> > ms;
ms convert(const mm& m)
{
ms r;
for (mm::const_iterator it = m.begin(); it != m.end(); ++it)
{
set<string>& s(r[it->first]);
s.insert(it->second);
}
return r;
}
int main()
{
mm m;
m.insert(make_pair("john", "kowalski"));
m.insert(make_pair("john", "smiths"));
m.insert(make_pair("mary", "doe"));
m.insert(make_pair("mary", "walker"));
ms s(convert(m));
for (ms::iterator it = s.begin(); it != s.end(); ++it)
{
cout << it->first << ": ";
set<string> &st(it->second);
copy(st.begin(), st.end(), ostream_iterator<string>(cout, ", "));
cout << endl;
}
return 0;
}
This will print:
john: kowalski, smiths,
mary: doe, walker,