Template Function thrust::partition(ForwardIterator, ForwardIterator, InputIterator, Predicate)¶

Function Documentation¶

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.

The following code snippet demonstrates how to use

partition to reorder a sequence so that even numbers precede odd numbers.

Return

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.

Pre

The ranges [first,last) and [stencil, stencil + (last - first)) shall not overlap.

Parameters

first: The beginning of the sequence to reorder.
last: The end of the sequence to reorder.
stencil: The beginning of the stencil sequence.
pred: A function object which decides to which partition each element of the sequence [first, last) belongs.

Template Parameters

ForwardIterator: is a model of Forward Iterator, and ForwardIterator is mutable.
InputIterator: is a model of Input Iterator, and InputIterator's value_type is convertible to Predicate's argument_type.
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[] = {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: http://www.sgi.com/tech/stl/partition.html
See: stable_partition
See: partition_copy