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std::partition_copy

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< cpp‎ | algorithm
Revision as of 22:45, 31 May 2013 by P12bot (Talk | contribs)

 
 
 
Defined in header <algorithm>
template< class InputIt, class OutputIt1,

          class OutputIt2, class UnaryPredicate >
std::pair<OutputIt1, OutputIt2>
     partition_copy(InputIt first, InputIt last,
                    OutputIt1 d_first_true, OutputIt2 d_first_false,

                    UnaryPredicate p);
(since C++11)

Copies the elements that satisfy the predicate p from the range [first, last) to the range beginning at d_first_true, and copies the elements that do not satisfy p to the range beginning at d_first_false.

Contents

Parameters

first, last - the range of elements to sort
d_first_true - the beginning of the output range for the elements that satisfy p
d_first_false - the beginning of the output range for the elements that do not satisfy p
p - unary predicate which returns ​true if the element should be placed in d_first_true.

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

 bool pred(const Type &a);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The type Type must be such that an object of type InputIt can be dereferenced and then implicitly converted to Type. ​

Type requirements
-
InputIt must meet the requirements of InputIterator.
-
OutputIt1 must meet the requirements of OutputIterator.
-
OutputIt2 must meet the requirements of OutputIterator.
-
UnaryPredicate must meet the requirements of Predicate.

Return value

A pair constructed from the iterator to the end of the d_first_true range and the iterator to the end of the d_first_false range.

Complexity

Exactly distance(first, last) applications of p.

Possible implementation

template<class InputIt, class OutputIt1,
         class OutputIt2, class UnaryPredicate>
std::pair<OutputIt1, OutputIt2>
    partition_copy(InputIt first, InputIt last,
                   OutputIt1 d_first_true, OutputIt2 d_first_false,
                   UnaryPredicate p)
{
    while (first != last) {
        if (p(*first)) {
            *d_first_true = *first;
            ++d_first_true;
        } else {
            *d_first_false = *first;
            ++d_first_false;
        }
        ++first;
    }
    return std::pair<OutputIt1, OutputIt2>(d_first_true, d_first_false);
}

Example

#include <iostream>
#include <algorithm>
#include <utility>
 
int main()
{
    int arr [10] = {1,2,3,4,5,6,7,8,9,10};
    int true_arr [5] = {0};
    int false_arr [5] = {0};
 
    std::partition_copy(std::begin(arr), std::end(arr), std::begin(true_arr),std::begin(false_arr),
                        [] (int i) {return i > 5;});
 
    std::cout << "true_arr: ";
    for (auto it = std::begin(true_arr); it != std::end(true_arr); ++it) {
        std::cout << *it << ' ';
    }
    std::cout << '\n'; 
 
    std::cout << "false_arr: ";
    for (auto it = std::begin(false_arr); it != std::end(false_arr); ++it) {
        std::cout << *it << ' ';
    }
    std::cout << '\n'; 
 
    return 0;
 
}

Output:

true_arr: 6 7 8 9 10
false_arr: 1 2 3 4 5

See also

divides a range of elements into two groups
(function template) [edit]
divides elements into two groups while preserving their relative order
(function template) [edit]