◆ gather_if() [3/4]

template<typename DerivedPolicy , typename InputIterator1 , typename InputIterator2 , typename RandomAccessIterator , typename OutputIterator , typename Predicate >
__host__ __device__ OutputIterator thrust::gather_if ( const thrust::detail::execution_policy_base< DerivedPolicy > &  exec,
InputIterator1  map_first,
InputIterator1  map_last,
InputIterator2  stencil,
RandomAccessIterator  input_first,
OutputIterator  result,
Predicate  pred 

gather_if conditionally copies elements from a source array into a destination range according to a map. For each input iterator i in the range [map_first, map_last) such that the value of pred(*(stencil + (i - map_first))) is true, the value input_first[*i] is assigned to *(result + (i - map_first)). RandomAccessIterator must permit random access.

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

execThe execution policy to use for parallelization.
map_firstBeginning of the range of gather locations.
map_lastEnd of the range of gather locations.
stencilBeginning of the range of predicate values.
input_firstBeginning of the source range.
resultBeginning of the destination range.
predPredicate to apply to the stencil values.
Template Parameters
DerivedPolicyThe name of the derived execution policy.
InputIterator1must be a model of Input Iterator and InputIterator1's value_type must be convertible to RandomAccessIterator's difference_type.
InputIterator2must be a model of Input Iterator and InputIterator2's value_type must be convertible to Predicate's argument_type.
RandomAccessIteratormust be a model of Random Access iterator and RandomAccessIterator's value_type must be convertible to OutputIterator's value_type.
OutputIteratormust be a model of Output Iterator.
Predicatemust be a model of Predicate.
The range [map_first, map_last) shall not overlap the range [result, result + (map_last - map_first)).
The range [stencil, stencil + (map_last - map_first)) shall not overlap the range [result, result + (map_last - map_first)).
The input data shall not overlap the range [result, result + (map_last - map_first)).
gather_if is the inverse of scatter_if.

The following code snippet demonstrates how to use gather_if to gather selected values from an input range based on an arbitrary selection function using the thrust::device execution policy for parallelization:

#include <thrust/gather.h>
struct is_even
__host__ __device__
bool operator()(const int x)
return (x % 2) == 0;
int values[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
thrust::device_vector<int> d_values(values, values + 10);
// we will select an element when our stencil is even
int stencil[10] = {0, 3, 4, 1, 4, 1, 2, 7, 8, 9};
thrust::device_vector<int> d_stencil(stencil, stencil + 10);
// map all even indices into the first half of the range
// and odd indices to the last half of the range
int map[10] = {0, 2, 4, 6, 8, 1, 3, 5, 7, 9};
thrust::device_vector<int> d_map(map, map + 10);
d_map.begin(), d_map.end(),
// d_output is now {0, 7, 4, 7, 8, 7, 3, 7, 7, 7}