thrust::gather_if

Defined in thrust/gather.h

template<typename DerivedPolicy, typename InputIterator1, typename InputIterator2, typename RandomAccessIterator, typename OutputIterator> 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)

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 *(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.

The following code snippet demonstrates how to use gather_if to gather selected values from an input range using the thrust::device execution policy:

Remark

gather_if is the inverse of scatter_if.

#include <thrust/gather.h>
#include <thrust/device_vector.h>
#include <thrust/execution_policy.h>
...

int values[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
thrust::device_vector<int> d_values(values, values + 10);

// select elements at even-indexed locations
int stencil[10] = {1, 0, 1, 0, 1, 0, 1, 0, 1, 0};
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);

thrust::device_vector<int> d_output(10, 7);
thrust::gather_if(thrust::device,
                  d_map.begin(), d_map.end(),
                  d_stencil.begin(),
                  d_values.begin(),
                  d_output.begin());
// d_output is now {0, 7, 4, 7, 8, 7, 3, 7, 7, 7}

Parameters

exec – The execution policy to use for parallelization.
map_first – Beginning of the range of gather locations.
map_last – End of the range of gather locations.
stencil – Beginning of the range of predicate values.
input_first – Beginning of the source range.
result – Beginning of the destination range.

Template Parameters

DerivedPolicy – The name of the derived execution policy.
InputIterator1 – must be a model of Input Iterator and InputIterator1's value_type must be convertible to RandomAccessIterator's difference_type.
InputIterator2 – must be a model of Input Iterator and InputIterator2's value_type must be convertible to bool.
RandomAccessIterator – must be a model of Random Access iterator and RandomAccessIterator's value_type must be convertible to OutputIterator's value_type.
OutputIterator – must be a model of Output Iterator.

Pre

The range [map_first, map_last) shall not overlap the range [result, result + (map_last - map_first)).

Pre

The range [stencil, stencil + (map_last - map_first)) shall not overlap the range [result, result + (map_last - map_first)).

Pre

The input data shall not overlap the range [result, result + (map_last - map_first)).