thrust::transform_if

Defined in thrust/transform.h

template<typename DerivedPolicy, typename InputIterator, typename ForwardIterator, typename UnaryFunction, typename Predicate> ForwardIterator thrust::transform_if(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator first, InputIterator last, 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 the input sequence satifies 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(*i) is evaluated. 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 to negate the odd-valued elements of a range 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};

struct is_odd
{
  __host__ __device__
  bool operator()(int x)
  {
    return x % 2;
  }
};

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

// negate odd elements
thrust::transform_if(thrust::host, data, data + 10, data, op, is_odd()); // in-place transformation

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