std::partial_sort_copy

 

C++

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Algorithm library

Functions
Non-modifying sequence operations
all_of any_of none_of (C++11) (C++11) (C++11) for_each count count_if mismatch equal	find find_if find_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copy copy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n remove remove_if remove_copy remove_copy_if	replace replace_if replace_copy replace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffle shuffle   (C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class InputIt, class RandomIt > RandomIt partial_sort_copy( InputIt first, InputIt last,                             RandomIt d_first, RandomIt d_last );	(1)
template< class InputIt, class RandomIt, class Compare > RandomIt partial_sort_copy( InputIt first, InputIt last,                             RandomIt d_first, RandomIt 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 not guaranteed to be preserved. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.

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 RandomIt can be dereferenced and then implicitly converted to both of them. ​
Type requirements
- InputIt must meet the requirements of InputIterator.
- RandomIt must meet the requirements of ValueSwappable and RandomAccessIterator.
- The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

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).

Complexity

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

Example

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

run this code

#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());
 
    std::cout << "Writing to the smaller vector in ascending order gives: ";
    for (int a : v1) {
        std::cout << a << " ";
    }
    std::cout << '\n';
    if(it == v1.end())
        std::cout << "The return value is the end iterator\n";
 
    it = std::partial_sort_copy(v0.begin(), v0.end(), v2.begin(), v2.end(), 
                                std::greater<int>());
 
    std::cout << "Writing to the larger vector in descending order gives: ";
    for (int a : v2) {
        std::cout << a << " ";
    }
    std::cout << '\n' << "The return value is the iterator to " << *it << '\n';
}

Output:

Writing to the smaller vector in ascending order gives: 1 2 3
The return value is the end iterator
Writing to the larger vector in descending order gives: 5 4 3 2 1 15 16
The return value is the iterator to 15

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)