stl::multimap - how do i get groups of data?
Solution 1:
pair<Iter, Iter> range = my_multimap.equal_range("Group1");
int total = accumulate(range.first, range.second, 0);
Is one way.
Edit:
If you don't know the group you are looking for, and are just going through each group, getting the next group's range can be done like so:
template <typename Pair>
struct Less : public std::binary_function<Pair, Pair, bool>
{
bool operator()(const Pair &x, const Pair &y) const
{
return x.first < y.first;
}
};
Iter first = mmap.begin();
Iter last = adjacent_find(first, mmap.end(), Less<MultimapType::value_type>());
Solution 2:
// samekey.cpp -- Process groups with identical keys in a multimap
#include <iostream>
#include <string>
#include <map>
using namespace std;
typedef multimap<string, int> StringToIntMap;
typedef StringToIntMap::iterator mapIter;
int main ()
{
StringToIntMap mymap;
mymap.insert(make_pair("Group2", 11));
mymap.insert(make_pair("Group1", 3));
mymap.insert(make_pair("Group2", 10));
mymap.insert(make_pair("Group1", 1));
mymap.insert(make_pair("Group2", 12));
mymap.insert(make_pair("Group1", 2));
cout << "mymap contains:" << endl;
mapIter m_it, s_it;
for (m_it = mymap.begin(); m_it != mymap.end(); m_it = s_it)
{
string theKey = (*m_it).first;
cout << endl;
cout << " key = '" << theKey << "'" << endl;
pair<mapIter, mapIter> keyRange = mymap.equal_range(theKey);
// Iterate over all map elements with key == theKey
for (s_it = keyRange.first; s_it != keyRange.second; ++s_it)
{
cout << " value = " << (*s_it).second << endl;
}
}
return 0;
} // end main
// end samekey.cpp