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std::ranges::partition_copy, std::ranges::partition_copy_result

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms: std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
C library
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
ranges::partition_copy
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutations
 
Defined in header <algorithm>
Call signature
template <std::input_iterator I, std::sentinel_for<I> S,

         std::weakly_incrementable O1, std::weakly_incrementable O2,
         class Proj = std::identity, std::indirect_unary_predicate<
         std::projected<I, Proj>> Pred>
requires std::indirectly_copyable<I, O1> && std::indirectly_copyable<I, O2>
constexpr ranges::partition_copy_result<I, O1, O2>

ranges::partition_copy( I first, S last, O1 out_true, O2 out_false, Pred pred, Proj proj = {} );
(1) (since C++20)
template<ranges::input_range R, std::weakly_incrementable O1, std::weakly_incrementable O2,

         class Proj = std::identity,
         std::indirect_unary_predicate<std::projected<iterator_t<R>, Proj>> Pred>
requires std::indirectly_copyable<ranges::iterator_t<R>, O1> &&
         std::indirectly_copyable<ranges::iterator_t<R>, O2>
constexpr ranges::partition_copy_result<ranges::borrowed_iterator_t<R>, O1, O2>

ranges::partition_copy( R&& r, O1 out_true, O2 out_false, Pred pred, Proj proj = {} );
(2) (since C++20)
Helper types
template<class I, class O1, class O2>
using partition_copy_result = ranges::in_out_out_result<I, O1, O2>;
(3) (since C++20)
1) Copies the elements from the input range [first, last) to two different output ranges depending on the value returned by the predicate pred. The projected by proj elements that satisfy the predicate pred are copied to the range beginning at out_true. The rest of the elements are copied to the range beginning at out_false.
Precondition: the input range does not overlap either of the output ranges.
2) Same as (1), but uses r as the soruce range, as if using ranges::begin(r) as first, and ranges::end(r) as last.

The function-like entities described on this page are niebloids, that is:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

[edit] Parameters

first, last - the input range of elements to copy from
r - the input range of elements to copy from
out_true - the beginning of the output range for the elements that satisfy pred
out_false - the beginning of the output range for the elements that do not satisfy pred
pred - predicate to apply to the projected elements
proj - projection to apply to the elements.

[edit] Return value

An object equal to {last, o1, o2}, where o1 and o2 are the ends of the output ranges respectivelly, after the copying is complete.

[edit] Complexity

Exactly ranges::distance(first, last) applications of the corresponding predicate comp and any projection proj.

[edit] Possible implementation

struct partition_copy_fn {
  template <std::input_iterator I, std::sentinel_for<I> S,
           std::weakly_incrementable O1, std::weakly_incrementable O2,
           class Proj = std::identity, std::indirect_unary_predicate<
           std::projected<I, Proj>> Pred>
  requires std::indirectly_copyable<I, O1> && std::indirectly_copyable<I, O2>
  constexpr ranges::partition_copy_result<I, O1, O2>
  operator()( I first, S last, O1 out_true, O2 out_false, Pred pred, Proj proj = {} ) const {
      for (; first != last; ++first)
          if (!!std::invoke(pred, std::invoke(proj, *first)))
              *out_true = *first, ++out_true;
          else
              *out_false = *first, ++out_false;
      return {std::move(first), std::move(out_true), std::move(out_false)};
  }
 
  template<ranges::input_range R, std::weakly_incrementable O1, std::weakly_incrementable O2,
           class Proj = std::identity,
           std::indirect_unary_predicate<std::projected<iterator_t<R>, Proj>> Pred>
  requires std::indirectly_copyable<ranges::iterator_t<R>, O1> &&
           std::indirectly_copyable<ranges::iterator_t<R>, O2>
  constexpr ranges::partition_copy_result<ranges::borrowed_iterator_t<R>, O1, O2>
  operator()( R&& r, O1 out_true, O2 out_false, Pred pred, Proj proj = {} ) const {
      return (*this)(ranges::begin(r), ranges::end(r), std::move(out_true),
                     std::move(out_false), std::move(pred), std::move(proj));
  }
};
 
inline constexpr partition_copy_fn partition_copy{};

[edit] Example

#include <algorithm>
#include <cctype>
#include <iostream>
#include <vector>
#include <iterator>
 
int main()
{
    const auto in = {'N', '3', 'U', 'M', '1', 'B', '4', 'E', '1', '5', 'R', '9'};
 
    std::vector<int> o1(size(in)), o2(size(in));
 
    auto pred = [](char c){ return std::isalpha(c); };
 
    auto ret = std::ranges::partition_copy(in, o1.begin(), o2.begin(), pred);
 
    std::cout << "in = ";
    std::ranges::copy(in, std::ostream_iterator<char>(std::cout, " "));
    std::cout << "\n" "o1 = ";
    std::copy(o1.begin(), ret.out1, std::ostream_iterator<char>(std::cout, " "));
    std::cout << "\n" "o2 = ";
    std::copy(o2.begin(), ret.out2, std::ostream_iterator<char>(std::cout, " "));
    std::cout << '\n';
}

Output:

in = N 3 U M 1 B 4 E 1 5 R 9
o1 = N U M B E R
o2 = 3 1 4 1 5 9

[edit] See also

divides a range of elements into two groups
(niebloid) [edit]
divides elements into two groups while preserving their relative order
(niebloid) [edit]
copies a range of elements to a new location
(niebloid) [edit]
copies a range of elements omitting those that satisfy specific criteria
(niebloid) [edit]
copies a range dividing the elements into two groups
(function template) [edit]