Template Function thrust::partition_copy(InputIterator, InputIterator, OutputIterator1, OutputIterator2, Predicate)¶

Function Documentation¶

template<typename InputIterator, typename OutputIterator1, typename OutputIterator2, typename Predicate> thrust::pair<OutputIterator1, OutputIterator2> thrust::partition_copy(InputIterator first, InputIterator last, OutputIterator1 out_true, OutputIterator2 out_false, Predicate pred)

partition_copy differs from partition only in that the reordered sequence is written to difference output sequences, rather than in place.

partition_copy copies the elements [first, last) based on the function object pred. All of the elements that satisfy pred are copied to the range beginning at out_true and all the elements that fail to satisfy it are copied to the range beginning at out_false.

The following code snippet demonstrates how to use

partition_copy to separate a sequence into two output sequences of even and odd numbers.

Return

A pair p such that p.first is the end of the output range beginning at out_true and p.second is the end of the output range beginning at out_false.

Pre

The input range shall not overlap with either output range.

Parameters

first: The beginning of the sequence to reorder.
last: The end of the sequence to reorder.
out_true: The destination of the resulting sequence of elements which satisfy pred.
out_false: The destination of the resulting sequence of elements which fail to satisfy pred.
pred: A function object which decides to which partition each element of the sequence [first, last) belongs.

Template Parameters

InputIterator: is a model of Input Iterator, and InputIterator's value_type is convertible to Predicate's argument_type and InputIterator's value_type is convertible to OutputIterator1 and OutputIterator2's value_types.
OutputIterator1: is a model of Output Iterator.
OutputIterator2: is a model of Output Iterator.
Predicate: is a model of Predicate.

#include <thrust/partition.h>
...
struct is_even
{
  __host__ __device__
  bool operator()(const int &x)
  {
    return (x % 2) == 0;
  }
};
...
int A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int result[10];
const int N = sizeof(A)/sizeof(int);
int *evens = result;
int *odds  = result + 5;
thrust::partition_copy(A, A + N, evens, odds, is_even());
// A remains {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
// result is now {2, 4, 6, 8, 10, 1, 3, 5, 7, 9}
// evens points to {2, 4, 6, 8, 10}
// odds points to {1, 3, 5, 7, 9}

Note: The relative order of elements in the two reordered sequences is not necessarily the same as it was in the original sequence. A different algorithm, stable_partition_copy, does guarantee to preserve the relative order.
See: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2569.pdf
See: stable_partition_copy
See: partition