std::partial_sort_copy

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Defined in header <algorithm>

template< class InputIterator, class RandomAccessIterator >

RandomAccessIterator partial_sort_copy( InputIterator first,
                                        InputIterator last,
                                        RandomAccessIterator d_first,

                                        RandomAccessIterator d_last );
(1)
template< class InputIterator, class RandomAccessIterator, class Compare >

RandomAccessIterator partial_sort_copy( InputIterator first,
                                        InputIterator last,
                                        RandomAccessIterator d_first,
                                        RandomAccessIterator d_last,

                                        Compare comp );
(2)

Sorts some of the elements in the range [first, last) in ascending order. At most d_first - d_last of the elements are moved to the range [d_first, d_first + n) and then sorted. n is the number of elements to sort (n = min(last - first, d_last - d_first)). The order of equal elements is guaranteed to be preserved. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.

Contents

[edit] Parameters

first, last - the range of elements to sort
d_first, d_last - random access iterators defining the destination range
comp - comparison function 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 must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type RandomAccessIterator can be dereferenced and then implicitly converted to both of them. ​

[edit] Return value

an iterator to the element defining the upper boundary of the sorted range, i.e. d_first + min(last - first, d_last - d_first).

[edit] Complexity

O(N·log(min(D,N)), where N = std::distance(first, last), D = std::distance(d_first, d_last) applications of cmp.

[edit] Example

The following code sorts an vector of integers and copies them into a smaller and a larger vector.

#include <algorithm>
#include <vector>
#include <functional>
#include <iostream>
 
int main()
{
    std::vector<int> v0{4, 2, 5, 1, 3};
    std::vector<int> v1(10, 11, 12);
    std::vector<int> v2{10, 11, 12, 13, 14, 15, 16};
    std::vector<int>::iterator it;
 
    it = std::partial_sort_copy(v0.begin(), v0.end(), v1.begin(), v1.end());
 
    for (int a : v1) {
	std::cout << a << " ";
    }
    std::cout << '\n' << *it << '\n';
 
    it = std::partial_sort_copy(v0.begin(), v0.end(), v1.begin(), v1.end(), 
                                std::greater<int>());
 
    for (int a : v1) {
	std::cout << a << " ";
    }
    std::cout << '\n' << *it << '\n';
}

Output:

1 2 3
3
1 2 3 4 5 15 16
15

[edit] See also

partial_sort
sorts the first N elements of a range
(function template)
sort
sorts a range into ascending order
(function template)
stable_sort
sorts a range of elements while preserving order between equal elements
(function template)