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std::nth_element

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Defined in header <algorithm>
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template< class RandomIt >
void nth_element( RandomIt first, RandomIt nth, RandomIt last );
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<td > (1) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl ">

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template< class RandomIt, class Compare >
void nth_element( RandomIt first, RandomIt nth, RandomIt last, Compare comp );
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<td > (2) </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end

Partially sorts the range [first, last) in ascending order so that all elements in the range [first, nth) are less than those in the range [nth, last). The first version uses operator< to compare the elements, the second version uses the given comparison function comp. The element placed in the nth position is exactly the element that would occur in this position if the range was fully sorted.

Contents

Parameters

first, last - random access iterators defining the range sort
nth - random access iterator defining the sort partition point
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than the second.

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function object must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
-
RandomIt must meet the requirements of ValueSwappable and RandomAccessIterator.
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The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

Linear in std::distance(first, last) on average.

Example

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
 
int main()
{
    std::vector<int> v{5, 6, 4, 3, 2, 6, 7, 9, 3};
 
    std::nth_element(v.begin(), v.begin() + v.size()/2, v.end());
    std::cout << "The median is " << v[v.size()/2] << '\n';
 
    std::nth_element(v.begin(), v.begin()+1, v.end(), std::greater<int>());
    std::cout << "The second largest element is " << v[1] << '\n';
}

Output:

The median is 5
The second largest element is 7

See also

Template:cpp/algorithm/dcl list partial sort copyTemplate:cpp/algorithm/dcl list stable sortTemplate:cpp/algorithm/dcl list sort