Stl multimap - how to get the list of values of all keys in the multimap

Question

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

What i want to do is to compute the list of values of every key stored in the multimap.

What have you tried? Have you even done any basic research into how to use a `multimap`? — Jonathan Wakely, Jun 23 '12 at 10:51
Have you understood my question? If you know the answer i would be pleased to hear... — Marco Masci, Jun 23 '12 at 10:54
Yes, I know the answer, but I'm not answering it because I think it's a lazy, poorly-researched question. It would be easy for you to find an answer yourself, if you made any effort. Google for "stl multimap" and you get how to iterate on a multimap as the **very first result** http://www.sgi.com/tech/stl/Multimap.html — Jonathan Wakely, Jun 23 '12 at 10:57
Wrong answer. You should read more carefully the question ( early, i have editated the title in order to express it more clearly). Consider that i do not know the keys... — Marco Masci, Jun 23 '12 at 11:15
That's why you should _iterate_. The example on the page I linked to shows how to print all the keys and values. Hmm, how could that possibly be helpful to get a list of all the keys and values? — Jonathan Wakely, Jun 23 '12 at 11:17

score 2 · Answer 1 · answered Jun 23 '12 at 09:35

2

Use equal_range(); it returns a pair of iterators describing the range of items with the specified key.

answered Jun 23 '12 at 09:35

Oliver Charlesworth

267,707
33
569
680

Ok thanks. But how to iterate over all keys? – Marco Masci Jun 23 '12 at 09:36
@MarcoMasci: Perhaps I misunderstand your original question. It sounds like you want to know all the values corresponding to a particular key. Do I understand correctly? – Oliver Charlesworth Jun 23 '12 at 09:39
No: i don't know the keys stored in it. I want to enumerate all keys stored in the multimap and, for every key, collect the associated values. – Marco Masci Jun 23 '12 at 09:41

score 2 · Answer 2 · answered Jun 23 '12 at 10:53

A generic answer to the generic question is:

template<class KEY, class VALUE>
std::vector<VALUE> getValues(const std::multimap<KEY,VALUE>& aMap){
    std::vector<VALUE> values;
    for(multimap<KEY,VALUE>::const_iterator it=aMap.begin(), end=aMap.end();it!=end;++it){
        values.push_back((*it).second);
    }
    return values;
}

score 0 · Answer 3 · answered Jun 23 '12 at 09:37

0

Something like that should work

multimap<string, int> m;
vector<int> values;

for (multimap<string, int>::iterator it = m.begin(); it != m.end(); ++it)
{
    values.push_back((*it).second);
}

answered Jun 23 '12 at 09:37

Miroslav Šiagi

64
4

Stl multimap - how to get the list of values of all keys in the multimap

3 Answers3