#include <string>
#include <unordered_set>
#include <utility>
#include<boost/unordered_map.hpp>

using namespace std;

int main()
{
    boost::unordered_map< unordered_set<string>, int> training_groups;
    pair<unordered_set<string>, int> a_training_group;
    training_groups.insert(a_training_group);
    return 0;
}

1>C:Program Files (x86)Microsoft Visual Studio 12.0VCincludexhash(30): error C2440: 'type cast' : cannot convert from 'const std::unordered_set<std::string,std::hash<_Kty>,std::equal_to<_Kty>,std::allocator<_Kty>>' to 'size_t'
1>          with
1>          [
1>              _Kty=std::string
1>          ]
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>          C:Program Filesboostboost_1_59_0boost/functional/hash/extensions.hpp(262) : see reference to function template instantiation 'size_t stdext::hash_value<T>(const _Kty &)' being compiled
1>          with
1>          [
1>              T=std::unordered_set<std::string,std::hash<std::string>,std::equal_to<std::string>,std::allocator<std::string>>
1>  ,            _Kty=std::unordered_set<std::string,std::hash<std::string>,std::equal_to<std::string>,std::allocator<std::string>>
1>          ]