partial sort a vector with lambda predicate

Question

I would like to partial sort this vector with a predicate as such

std::vector<std::pair<std::string, int>> vp;

        std::partial_sort(vp.begin(), vp.begin()+10, [](const std::pair<std::string,int> &left, const std::pair<std::string,int> &right)
        {
            return left.second > right.second;
        });

However I get the error

 no matching function for call to ‘partial_sort(std::vector<std::pair<std::basic_string<char>, int> >::iterator, __gnu_cxx::__normal_iterator<std::pair<std::basic_string<char>, int>*, ....

The above works fine for std::sort and not for partial_sort any suggestions ?

Care to provde the ...? Does it list candidate functions considered and reasons why they were not applicable? — Angew is no longer proud of SO
– Angew is no longer proud of SO, Commented Dec 2, 2014 at 8:03

Angew is no longer proud of SO · Accepted Answer · 2014-12-02 08:06:24Z

4

Looking at some reference documentation, you will find that std::partial_sort requires 3 iterators, not 2: start, middle and end. It will re-arrange the range so that the range [start, middle) is sorted, and contains the smallest elements from the range [start, end).

Depending on what exactly you're trying to achieve, you need to provide an appropriate 3rd iterator. If you're trying to find the 10 smallest elements, just do this:

std::partial_sort(vp.begin(), vp.begin()+10, vp.end(), /*lambda as before*/);

answered Dec 2, 2014 at 8:06

Angew is no longer proud of SO

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