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Difference between revisions of "cpp/algorithm/partial sort"

From cppreference.com
< cpp‎ | algorithm
(Added external links)
m (Use parallel overload precondition template)
Line 38: Line 38:
 
@1@ Elements are compared using {{tt|operator<}}.
 
@1@ Elements are compared using {{tt|operator<}}.
 
@3@ Elements are compared using the given binary comparison function {{tt|comp}}.
 
@3@ Elements are compared using the given binary comparison function {{tt|comp}}.
−
@2,4@ Same as {{v|1,3}}, but executed according to {{tt|policy}}. These overloads do not participate in overload resolution unless {{c|std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>}} is true
+
@2,4@ Same as {{v|1,3}}, but executed according to {{tt|policy}}. {{cpp/algorithm/parallel overload precondition|plural=true}}
  
 
===Parameters===
 
===Parameters===

Revision as of 05:11, 14 April 2020

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
(1)
template< class RandomIt >
void partial_sort( RandomIt first, RandomIt middle, RandomIt last );
 (until C++20)
template< class RandomIt >
constexpr void partial_sort( RandomIt first, RandomIt middle, RandomIt last );
 (since C++20)
template< class ExecutionPolicy, class RandomIt >

void partial_sort( ExecutionPolicy&& policy,

                   RandomIt first, RandomIt middle, RandomIt last );
 (2) (since C++17)
(3)
template< class RandomIt, class Compare >

void partial_sort( RandomIt first, RandomIt middle, RandomIt last,

                   Compare comp );
 (until C++20)
template< class RandomIt, class Compare >

constexpr void partial_sort( RandomIt first, RandomIt middle, RandomIt last,

                             Compare comp );
 (since C++20)
template< class ExecutionPolicy, class RandomIt, class Compare >

void partial_sort( ExecutionPolicy&& policy,
                   RandomIt first, RandomIt middle, RandomIt last,

                   Compare comp );
 (4) (since C++17)

Rearranges elements such that the range [first, middle) contains the sorted middle - first smallest elements in the range [first, last).

The order of equal elements is not guaranteed to be preserved. The order of the remaining elements in the range [middle, last) is unspecified.

1) Elements are compared using operator<.
3) Elements are compared using the given binary comparison function comp.
2,4) Same as (1,3), but executed according to policy. These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)

Contents

Parameters

first, last - random access iterators defining the range
middle - random access iterator defining the last element to be sorted
policy - the execution policy to use. See execution policy for details.
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than (i.e. is ordered before) the second.

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

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

While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy(since C++11)).
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 LegacyRandomAccessIterator.
-
The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

Approximately (last-first)log(middle-first) applications of cmp

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

See also the implementations in libstdc++ and libc++.

Example

Run this code
#include <algorithm>
#include <functional>
#include <array>
#include <iostream>
 
int main()
{
    std::array<int, 10> s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
 
    std::partial_sort(s.begin(), s.begin() + 3, s.end());
    for (int a : s) {
        std::cout << a << " ";
    } 
}

Possible output: 

0 1 2 7 8 6 5 9 4 3

See also

 partially sorts the given range making sure that it is partitioned by the given element
(function template) [edit]
copies and partially sorts a range of elements
(function template) [edit]
sorts a range of elements while preserving order between equal elements
(function template) [edit]
sorts a range into ascending order
(function template) [edit]
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