Template Function thrust::copy_if(InputIterator1, InputIterator1, InputIterator2, OutputIterator, Predicate)

Function Documentation

template<typename InputIterator1, typename InputIterator2, typename OutputIterator, typename Predicate>
OutputIterator thrust::copy_if(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 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:

Return

result + n, where n is equal to the number of times pred evaluated to true in the range [stencil, stencil + (last-first)).

Pre

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

Pre

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

Parameters

• first: The beginning of the sequence from which to copy.

• last: The end of the sequence from which to copy.

• stencil: The beginning of the stencil sequence.

• result: The beginning of the sequence into which to copy.

• pred: The predicate to test on every value of the range [stencil, stencil + (last-first)).

Template Parameters

• InputIterator1: is a model of Input Iterator.

• InputIterator2: is a model of Input Iterator, and InputIterator2's value_type is convertible to Predicate's argument_type.

• OutputIterator: is a model of Output Iterator.

• Predicate: is a model of Predicate.

#include <thrust/copy.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(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}

See

remove_copy_if