thrust::transform_if

Defined in thrust/transform.h

template<typename DerivedPolicy, typename InputIterator1, typename InputIterator2, typename ForwardIterator, typename UnaryFunction, typename Predicate> ForwardIterator thrust::transform_if(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator1 first, InputIterator1 last, InputIterator2 stencil, ForwardIterator result, UnaryFunction op, Predicate pred)

This version of transform_if conditionally applies a unary function to each element of an input sequence 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 [first, last) the predicate pred(*s) is evaluated, where s is the corresponding input iterator in the range [stencil, stencil + (last - first) ). If this predicate evaluates to true, the result of op(*i) is assigned to *o, where o is the corresponding output iterator in the range [result, result + (last - first) ). Otherwise, op(*i) 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 data[10]    = {-5, 0, 2, -3, 2, 4, 0, -1, 2, 8};
int stencil[10] = { 1, 0, 1,  0, 1, 0, 1,  0, 1, 0};

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

thrust::transform_if(thrust::host, data, data + 10, stencil, data, op, identity); // in-place transformation

// data is now {5, 0, -2, -3, -2,  4, 0, -1, -2,  8};