thrust::copy_if

Defined in thrust/copy.h

template<typename DerivedPolicy, typename InputIterator1, typename InputIterator2, typename OutputIterator, typename Predicate> OutputIterator thrust::copy_if(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator1 first, InputIterator1 last, InputIterator2 stencil, OutputIterator result, Predicate pred)

This version of copy_if copies elements from the range [first,last) to a range beginning at result, except that any element whose corresponding stencil element causes pred to be false is not copied. copy_if is stable, meaning that the relative order of elements that are copied is unchanged.

More precisely, for every integer n such that 0 <= n < last-first, copy_if performs the assignment *result = *(first+n) and result is advanced one position if pred(*(stencil+n)). Otherwise, no assignment occurs and result is not advanced.

The algorithm’s execution is parallelized as determined by exec.

The following code snippet demonstrates how to use copy_if to perform stream compaction to copy numbers to an output range when corresponding stencil elements are even using the thrust::host execution policy:

#include <thrust/copy.h>
#include <thrust/execution_policy.h>
...
struct is_even
{
  __host__ __device__
  bool operator()(const int x)
  {
    return (x % 2) == 0;
  }
};
...
int N = 6;
int data[N]    = { 0, 1,  2, 3, 4, 5};
int stencil[N] = {-2, 0, -1, 0, 1, 2};
int result[4];

thrust::copy_if(thrust::host, data, data + N, stencil, result, is_even());

// data remains    = { 0, 1,  2, 3, 4, 5};
// stencil remains = {-2, 0, -1, 0, 1, 2};
// result is now     { 0, 1,  3, 5}