thrust::stable_partition

Defined in thrust/partition.h

template<typename ForwardIterator, typename Predicate> ForwardIterator thrust::stable_partition(ForwardIterator first, ForwardIterator last, Predicate pred)

stable_partition is much like partition : it reorders the elements in the range [first, last) based on the function object pred, such that all of the elements that satisfy pred precede all of the elements that fail to satisfy it. The postcondition is that, for some iterator middle in the range [first, last), pred(*i) is true for every iterator i in the range [first,middle) and false for every iterator i in the range [middle, last). The return value of stable_partition is middle.

stable_partition differs from partition in that stable_partition is guaranteed to preserve relative order. That is, if x and y are elements in [first, last), and stencil_x and stencil_y are the stencil elements in corresponding positions within [stencil, stencil + (last - first)), and pred(stencil_x) == pred(stencil_y), and if x precedes y, then it will still be true after stable_partition that x precedes y.

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

#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};
const int N = sizeof(A)/sizeof(int);
thrust::stable_partition(A, A + N,
                          is_even());
// A is now {2, 4, 6, 8, 10, 1, 3, 5, 7, 9}