You forgot the
list
. Try, for instance
#include <iostream>
#include <map>
#include <tuple>
#include <list>
using namespace std;
int main()
{
std::map<int, list<std::tuple<int, int> >> groups;
groups[0] = list<std::tuple<int,int>>{make_tuple(3,4)};
cout << get<1>(groups[0].front()) << endl;
}