std::ranges::partial_sort_copy, std::ranges::partial_sort_copy_result

 

C++

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Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges(C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)   execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)    (C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
Numeric operations
iota (C++11) inner_product adjacent_difference    accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17)    exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

Constrained algorithms

All names in this menu belong to namespace std::ranges

Non-modifying sequence operations

all_ofany_ofnone_of for_each for_each_n    countcount_if adjacent_find mismatch equal lexicographical_compare    containscontains_subrange (C++23)(C++23) findfind_iffind_if_not find_lastfind_last_iffind_last_if_not (C++23)(C++23)(C++23)   find_end find_first_of search search_n starts_with (C++23) ends_with (C++23)

Modifying sequence operations

copycopy_if copy_n copy_backward    move move_backward shift_leftshift_right (C++23)(C++23)   fill fill_n generate generate_n    transform swap_ranges    shuffle sample removeremove_if replacereplace_if reverse rotate remove_copyremove_copy_if    unique replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy

Partitioning operations

is_partitioned    partition_point    partition    partition_copy    stable_partition

Sorting operations

is_sorted is_sorted_until     sort stable_sort         partial_sort       nth_element partial_sort_copy

Binary search operations (on sorted ranges)

lower_bound         upper_bound         binary_search      equal_range

Set operations (on sorted ranges)

merge inplace_merge       set_difference set_intersection    set_union          includes set_symmetric_difference

Heap operations

is_heap is_heap_until       make_heap           sort_heap push_heap pop_heap

Minimum/maximum operations

max max_element         min min_element         minmax minmax_element     clamp

Permutation operations

is_permutation      next_permutation    prev_permutation

Fold operations

fold_left (C++23) fold_left_first (C++23)   fold_right (C++23) fold_right_last (C++23)   fold_left_with_iter (C++23) fold_left_first_with_iter (C++23)

Numeric operations iota (C++23)             Random number generation generate_random (C++26)

Operations on uninitialized storage

construct_at    destroy destroy_n destroy_at uninitialized_copy    uninitialized_move uninitialized_fill uninitialized_copy_n    uninitialized_move_n uninitialized_fill_n uninitialized_default_construct uninitialized_default_construct_n uninitialized_value_construct uninitialized_value_construct_n

Return types

in_fun_result in_in_result in_found_result    in_out_result in_in_out_result    in_out_out_result    min_max_result out_value_result (C++23) in_value_result (C++23)

 

Defined in header <algorithm>
Call signature
template<std::input_iterator I1, std::sentinel_for<I1> S1,           std::random_access_iterator I2, std::sentinel_for<I2> S2,           class Comp =ranges::less, class Proj1 =std::identity,           class Proj2 =std::identity> requires std::indirectly_copyable<I1, I2>&&          std::sortable<I2, Comp, Proj2>&&          std::indirect_strict_weak_order<Comp, std::projected<I1, Proj1>,              std::projected<I2, Proj2>> constexpr partial_sort_copy_result<I1, I2>     partial_sort_copy( I1 first, S1 last, I2 result_first, S2 result_last,                        Comp comp ={}, Proj1 proj1 ={}, Proj2 proj2 ={});	(1)	(since C++20)
template<ranges::input_range R1, ranges::random_access_range R2,           class Comp =ranges::less, class Proj1 =std::identity,           class Proj2 =std::identity> requires std::indirectly_copyable<ranges::iterator_t<R1>, ranges::iterator_t<R2>>&&          std::sortable<ranges::iterator_t<R2>, Comp, Proj2>&&          std::indirect_strict_weak_order<Comp, std::projected<ranges::iterator_t<R1>,              Proj1>, std::projected<ranges::iterator_t<R2>, Proj2>> constexpr partial_sort_copy_result<ranges::borrowed_iterator_t<R1>,                                    ranges::borrowed_iterator_t<R2>>     partial_sort_copy( R1&& r, R2&& result_r,                        Comp comp ={}, Proj1 proj1 ={}, Proj2 proj2 ={});	(2)	(since C++20)
Helper types
template<class I, class O > using partial_sort_copy_result =ranges::in_out_result<I, O>;	(3)	(since C++20)

Copies the first N elements from the source range [first, last), as if it was partially sorted with respect to comp and proj1, into the destination range [result_first, result_first + N), where \(\scriptsize N = \min{(L_1, L_2)}\)N = min(L₁, L₂), \(\scriptsize L_1\)L₁ is equal to ranges::distance(first, last), and \(\scriptsize L_2\)L₂ is equal to ranges::distance(result_first, result_last).

The order of equal elements is not guaranteed to be preserved.

1) The source range elements are projected using the function object proj1, and the destination elements are projected using the function object proj2.

2) Same as (1), but uses r as the source range and result_r as the destination range, as if using ranges::begin(r) as first, ranges::end(r) as last, ranges::begin(result_r) as result_first, and ranges::end(result_r) as result_last.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

Parameters

first, last	-	the iterator-sentinel pair defining the source range of elements to copy from
r	-	the source range to copy from
result_first, result_last	-	the iterator-sentinel pair defining the destination range of elements
result_r	-	the destination range
comp	-	comparison to apply to the projected elements
proj1	-	projection to apply to the elements of source range
proj2	-	projection to apply to the elements of destination range

Return value

An object equal to {last, result_first + N}.

Complexity

At most \(\scriptsize L_1 \cdot \log{(N)}\)L₁•log(N) comparisons and \(\scriptsize 2 \cdot L_1 \cdot \log{(N)}\)2•L₁•log(N) projections.

Possible implementation

struct partial_sort_copy_fn {template<std::input_iterator I1, std::sentinel_for<I1> S1, std::random_access_iterator I2, std::sentinel_for<I2> S2, class Comp =ranges::less, class Proj1 =std::identity, class Proj2 =std::identity> requires std::indirectly_copyable<I1, I2>&&std::sortable<I2, Comp, Proj2>&&std::indirect_strict_weak_order<Comp, std::projected<I1, Proj1>, std::projected<I2, Proj2>>constexpr ranges::partial_sort_copy_result<I1, I2> operator()(I1 first, S1 last, I2 result_first, S2 result_last, Comp comp ={}, Proj1 proj1 ={}, Proj2 proj2 ={})const{if(result_first == result_last)return{std::move(ranges::next(std::move(first), std::move(last))), std::move(result_first)};   auto out_last{result_first};// copy first N elementsfor(;!(first == last or out_last == result_last);++out_last, ++first)*out_last =*first;   // convert N copied elements into a max-heapranges::make_heap(result_first, out_last, comp, proj2);   // process the rest of the input range (if any), preserving the heap propertyfor(; first != last;++first){if(std::invoke(comp, std::invoke(proj1, *first), std::invoke(proj2, *result_first))){// pop out the biggest item and push in a newly found smaller oneranges::pop_heap(result_first, out_last, comp, proj2);*(out_last -1)=*first;ranges::push_heap(result_first, out_last, comp, proj2);}}   // first N elements in the output range is still// a heap - convert it into a sorted rangeranges::sort_heap(result_first, out_last, comp, proj2);   return{std::move(first), std::move(out_last)};}   template<ranges::input_range R1, ranges::random_access_range R2, class Comp =ranges::less, class Proj1 =std::identity, class Proj2 =std::identity> requires std::indirectly_copyable<ranges::iterator_t<R1>, ranges::iterator_t<R2>>&&std::sortable<ranges::iterator_t<R2>, Comp, Proj2>&&std::indirect_strict_weak_order<Comp, std::projected<ranges::iterator_t<R1>, Proj1>, std::projected<ranges::iterator_t<R2>, Proj2>>constexpr ranges::partial_sort_copy_result<ranges::borrowed_iterator_t<R1>, ranges::borrowed_iterator_t<R2>> operator()(R1&& r, R2&& result_r, Comp comp ={}, Proj1 proj1 ={}, Proj2 proj2 ={})const{return(*this)(ranges::begin(r), ranges::end(r), ranges::begin(result_r), ranges::end(result_r), std::move(comp), std::move(proj1), std::move(proj2));}};   inlineconstexpr partial_sort_copy_fn partial_sort_copy {};

Example

Run this code

#include <algorithm>#include <forward_list>#include <functional>#include <iostream>#include <ranges>#include <string_view>#include <vector>   void print(std::string_view rem, std::ranges::input_rangeautoconst& v){for(std::cout<< rem;constauto& e : v)std::cout<< e <<' ';std::cout<<'\n';}   int main(){conststd::forward_list source{4, 2, 5, 1, 3};   print("Write to the smaller vector in ascending order: ", "");   std::vector dest1{10, 11, 12}; print("const source list: ", source); print("destination range: ", dest1); std::ranges::partial_sort_copy(source, dest1); print("partial_sort_copy: ", dest1);   print("Write to the larger vector in descending order:", "");   std::vector dest2{10, 11, 12, 13, 14, 15, 16}; print("const source list: ", source); print("destination range: ", dest2); std::ranges::partial_sort_copy(source, dest2, std::greater{}); print("partial_sort_copy: ", dest2);}

Output:

Write to the smaller vector in ascending order: const source list: 4 2 5 1 3 destination range: 10 11 12 partial_sort_copy: 1 2 3 Write to the larger vector in descending order: const source list: 4 2 5 1 3 destination range: 10 11 12 13 14 15 16 partial_sort_copy: 5 4 3 2 1 15 16

See also

ranges::partial_sort (C++20)	sorts the first N elements of a range (algorithm function object)
ranges::sort (C++20)	sorts a range into ascending order (algorithm function object)
ranges::stable_sort (C++20)	sorts a range of elements while preserving order between equal elements (algorithm function object)
ranges::sort_heap (C++20)	turns a max heap into a range of elements sorted in ascending order (algorithm function object)
ranges::make_heap (C++20)	creates a max heap out of a range of elements (algorithm function object)
ranges::push_heap (C++20)	adds an element to a max heap (algorithm function object)
ranges::pop_heap (C++20)	removes the largest element from a max heap (algorithm function object)
partial_sort_copy	copies and partially sorts a range of elements (function template)