thrust

◆ partition_copy() [2/4]

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.

Parameters
firstThe beginning of the sequence to reorder.
lastThe end of the sequence to reorder.
out_trueThe destination of the resulting sequence of elements which satisfy pred.
out_falseThe destination of the resulting sequence of elements which fail to satisfy pred.
predA function object which decides to which partition each element of the sequence [first, last) belongs.
Returns
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.
Template Parameters
InputIteratoris 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.
OutputIterator1is a model of Output Iterator.
OutputIterator2is a model of Output Iterator.
Predicateis a model of Predicate.
Precondition
The input range shall not overlap with either output range.

The following code snippet demonstrates how to use partition_copy to separate a sequence into two output sequences of even and odd numbers.

...
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 also
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2569.pdf
stable_partition_copy
partition