thrust::copy_if

Defined in thrust/copy.h

template<typename DerivedPolicy, typename InputIterator, typename OutputIterator, typename Predicate> OutputIterator thrust::copy_if(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator first, InputIterator last, 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 which 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(*(first+n)). Otherwise, no assignment occurs and result is not advanced.

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

The following code snippet demonstrates how to use copy_if to perform stream compaction to copy even numbers to an output range using the thrust::host parallelization policy:

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

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

// V remains {-2, 0, -1, 0, 1, 2}
// result is now {-2, 0, 0, 2}