How is the C++ multimap container implemented?

The C++ standard does not define how the standard containers should be implemented, it only gives certain constraints like the one you say for vectors. multimaps have certain runtime complexity (O(lg n) for the interesting operations) and other guarantees, and can be implemented as red-black trees. This is how they are implemented in the GNU … Read more

stl::multimap – how do i get groups of data?

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 … Read more

is there an iterator across unique keys in a std::multimap?

You can use upper_bound to increment the iterator position instead of ++: #include <map> #include <string> #include <iostream> using namespace std; int main() { multimap<int,string> mm; mm.insert(make_pair(1, “a”)); mm.insert(make_pair(1, “lemon”)); mm.insert(make_pair(2, “peacock”)); mm.insert(make_pair(3, “angel”)); for( auto it = mm.begin(), end = mm.end(); it != end; it = mm.upper_bound(it->first) ) cout << it->first << ‘ ‘ … Read more

How to create a Multimap from a Map?

Assuming you have Map<String, Collection<String>> map = …; Multimap<String, String> multimap = ArrayListMultimap.create(); Then I believe this is the best you can do for (String key : map.keySet()) { multimap.putAll(key, map.get(key)); } or the more optimal, but harder to read for (Entry<String, Collection<String>> entry : map.entrySet()) { multimap.putAll(entry.getKey(), entry.getValue()); }

multimap in .NET

Because it’s almost christmas 🙂 ////////////////////////////////////////////////////////////////////// // Algorithmia is (c) 2008 Solutions Design. All rights reserved. // http://www.sd.nl ////////////////////////////////////////////////////////////////////// // COPYRIGHTS: // Copyright (c) 2008 Solutions Design. All rights reserved. // // The Algorithmia library sourcecode and its accompanying tools, tests and support code // are released under the following license: (BSD2) // ———————————————————————- // … Read more