multimap

I'm wondering which is more efficient. std::map< String, std::set<int> > or std::multimap< String, int > EDIT: I do not plan on doing anything out of the ordinary with these maps. Standard insert, delete, modify, search. The size of each set or multi keyed String shouldn't be more than 100. This I believe is implementation dependant, but an (un)educated guess: In practice it depends on the number of integers that you will be keeping in the multimap or the std::set . A multimap will most likely use a linear search of the values after the log(n) search of the key. If you have a large number of

As the question states ... I don't get the point about multiset s / multimap s . So, what's the purpose? Some use cases: multimap With ZIP code as a key, all people which have that ZIP code With account ID as key, all open orders of that person/account A dictionary, with per keyword various explanations multiset is in essence a map with a key and a integer count. The inventory of a shop, all products have their key and the amount still available is the value accumulated sales data of a shop, every time a product is sold the product id get's added to the multiset thereby increasing the amount

I have a multimap and I want get all the unique keys in it to be stored in a vector. multimap<char,int> mymm; multimap<char,int>::iterator it; char c; mymm.insert(pair<char,int>('x',50)); mymm.insert(pair<char,int>('y',100)); mymm.insert(pair<char,int>('y',150)); mymm.insert(pair<char,int>('y',200)); mymm.insert(pair<char,int>('z',250)); mymm.insert(pair<char,int>('z',300)); How can I do this? there is way to count number of elements with a key but none to count number of unique keys in a multimap. Added: By unique I mean all the keys in multimap once - they can be repeated or occur once in

I don't understand why multimap exists if we can create map of vectors or map of sets. For me only differences are: using equal_range in multimap for getting elements of a key and in map of vectors we simply use [] operator and have vector of elements. using multimap.insert(make_pair(key,value)) in multimap for adding elements and map_of_vectors[key].push_back(value) in map of vectors. So why use multimap? For me it's better to have a vector than two iterators to get all values of a key. This question applies also to unordered_map of vectors and unordered_multimap. I would say it depends on

Possible Duplicate: C# Sortable collection which allows duplicate keys Basically I'd like to make a Dictionary work with duplicate keys without going into custom comparer implementations. There is an idea of: Dictionary<key, List<value>> but it still has some overhead. I wish Dictionary had "AllowDuplicates". If you're using .NET 3.5 then Lookup is probably what you're after. .NET 2.0: PowerCollections contains the OrderedMultiDictionary . You still can use SortedList and try to make a unique key by combining your value and a Guid into a class. In this case, you must implement the IComparer

I initially started out using a std::multimap to store many values with the same key, but then I discovered that it doesn't preserve the insertion order among values with the same key. This answer claims it can be done with boost::multi_index::multi_index_container , but gives no example. Looking through the docs, there are no examples of that usage, and I can't make heads or tails of how you're supposed to use this thing. I have come to expect poor documentation from the lesser-used boost libraries, but this takes the cake. Can anyone point me to a tutorial or example that shows it used the