Intersection between various values from boost::bimap

Question

I am trying to use boost::bimap for one of my requirements. Below is sample code

typedef bimap<
        multiset_of< string >,
        multiset_of< string >,
        set_of_relation<>
        > bm_type;

 bm_type bm;

 assign::insert( bm )

 ( "John" , string("lazarus" ) )
 ( "Peter", string("vinicius") )
 ( "Peter", string("test") )
 ( "Simon", string("vinicius") )
 ( "John", string("viniciusa") )
 ( "John", string("vinicius") )

I would like to do something as finding matching values for John & Peter, in other words intersection between values for John & Peter for ex: In this case it will be ("vinicius"). Can someone provide some limelight over it?

Answer 1

Here's what I came up with initially:

template <typename Value = std::string, typename Bimap, typename Key>
std::set<Value> projection(Bimap const& bm, Key const& key)
{
    std::set<Value> p;
    auto range  = bm.left.equal_range(key);
    auto values = boost::make_iterator_range(range.first, range.second);

    for (auto& relation : values)
        p.insert(relation.template get<boost::bimaps::member_at::right>());

    return p;
}

auto john  = projection(bm, "John");
auto peter = projection(bm, "Peter");

std::multiset<std::string> intersection;
std::set_intersection(
         john.begin(), john.end(),
         peter.begin(), peter.end(),
         inserter(intersection, intersection.end())
     );

I think it can be more efficient. So I tried replacing the projection on the fly using Boost Range's adaptors:

struct GetRightMember
{
    template <typename> struct result { typedef std::string type; };

    template <typename T>
    std::string operator()(T const& v) const {
        return v.template get<boost::bimaps::member_at::right>();
    }
};

const GetRightMember getright;
std::cout << "Intersection: ";

// WARNING: broken: ranges not sorted
boost::set_intersection(
        bm.left.equal_range("John")  | transformed(getright),
        bm.left.equal_range("Peter") | transformed(getright),
        std::ostream_iterator<std::string>(std::cout, " "));

Sadly it doesn't work - presumably because the transformed ranges aren't sorted.

So I'd stick with the more verbose version (or reconsider my data structure choices). See it Live On Coliru