thrust

◆ partition() [4/4]

template<typename ForwardIterator , typename InputIterator , typename Predicate >
ForwardIterator thrust::partition ( ForwardIterator  first,
ForwardIterator  last,
InputIterator  stencil,
Predicate  pred 
)

partition reorders the elements [first, last) based on the function object pred applied to a stencil range [stencil, stencil + (last - first)), such that all of the elements whose corresponding stencil element satisfies pred precede all of the elements whose corresponding stencil element fails to satisfy it. The postcondition is that, for some iterator middle in the range [first, last), pred(*stencil_i) is true for every iterator stencil_i in the range [stencil,stencil + (middle - first)) and false for every iterator stencil_i in the range [stencil + (middle - first), stencil + (last - first)). The return value of stable_partition is middle.

Note that 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, does guarantee to preserve the relative order.

Parameters
firstThe beginning of the sequence to reorder.
lastThe end of the sequence to reorder.
stencilThe beginning of the stencil sequence.
predA function object which decides to which partition each element of the sequence [first, last) belongs.
Returns
An iterator referring to the first element of the second partition, that is, the sequence of the elements whose stencil elements do not satisfy pred.
Template Parameters
ForwardIteratoris a model of Forward Iterator, and ForwardIterator is mutable.
InputIteratoris a model of Input Iterator, and InputIterator's value_type is convertible to Predicate's argument_type.
Predicateis a model of Predicate.
Precondition
The ranges [first,last) and [stencil, stencil + (last - first)) shall not overlap.

The following code snippet demonstrates how to use partition to reorder a sequence so that even numbers precede odd numbers.

...
struct is_even
{
__host__ __device__
bool operator()(const int &x)
{
return (x % 2) == 0;
}
};
...
int A[] = {0, 1, 0, 1, 0, 1, 0, 1, 0, 1};
int S[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
const int N = sizeof(A)/sizeof(int);
thrust::partition(A, A + N, S, is_even());
// A is now {1, 1, 1, 1, 1, 0, 0, 0, 0, 0}
// S is unmodified
See also
http://www.sgi.com/tech/stl/partition.html
stable_partition
partition_copy