thrust::transform_if

Defined in thrust/transform.h

template<typename DerivedPolicy, typename InputIterator1, typename InputIterator2, typename InputIterator3, typename ForwardIterator, typename BinaryFunction, typename Predicate> ForwardIterator thrust::transform_if(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator3 stencil, ForwardIterator result, BinaryFunction binary_op, Predicate pred)

This version of transform_if conditionally applies a binary function to each pair of elements from two input sequences and stores the result in the corresponding position in an output sequence if the corresponding position in a stencil sequence satisfies a predicate. Otherwise, the corresponding position in the output sequence is not modified.

Specifically, for each iterator i in the range [first1, last1) and j = first2 + (i - first1) in the range [first2, first2 + (last1 - first1) ), the predicate pred(*s) is evaluated, where s is the corresponding input iterator in the range [stencil, stencil + (last1 - first1) ). If this predicate evaluates to true, the result of binary_op(*i,*j) is assigned to *o, where o is the corresponding output iterator in the range [result, result + (last1 - first1) ). Otherwise, binary_op(*i,*j) is not evaluated and no assignment occurs. The input and output sequences may coincide, resulting in an in-place transformation.

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

The following code snippet demonstrates how to use transform_if using the thrust::host execution policy for parallelization:

#include <thrust/transform.h>
#include <thrust/functional.h>
#include <thrust/execution_policy.h>
...

int input1[6]  = {-5,  0,  2,  3,  2,  4};
int input2[6]  = { 3,  6, -2,  1,  2,  3};
int stencil[8] = { 1,  0,  1,  0,  1,  0};
int output[6];

thrust::plus<int> op;
thrust::identity<int> identity;

thrust::transform_if(thrust::host, input1, input1 + 6, input2, stencil, output, op, identity);

// output is now {-2,  0,  0,  3,  4,  4};