TheRock/rocm-libraries/projects/rocthrust/examples/stream_compaction.cu

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#include <thrust/copy.h>
#include <thrust/count.h>
#include <thrust/device_vector.h>
#include <thrust/remove.h>
#include <thrust/sequence.h>

#include <iostream>
#include <iterator>
#include <string>

#include "include/host_device.h"

// this functor returns true if the argument is odd, and false otherwise
template <typename T>
struct is_odd
{
  __host__ __device__ bool operator()(T x)
  {
    return x % 2;
  }
};

template <typename Iterator>
void print_range(const std::string& name, Iterator first, Iterator last)
{
  using T = typename std::iterator_traits<Iterator>::value_type;

  std::cout << name << ": ";
  thrust::copy(first, last, std::ostream_iterator<T>(std::cout, " "));
  std::cout << "\n";
}

int main(void)
{
  // input size
  size_t N = 10;

  // define some types
  using Vector   = thrust::device_vector<int>;
  using Iterator = Vector::iterator;

  // allocate storage for array
  Vector values(N);

  // initialize array to [0, 1, 2, ... ]
  thrust::sequence(values.begin(), values.end());

  print_range("values", values.begin(), values.end());

  // allocate output storage, here we conservatively assume all values will be copied
  Vector output(values.size());

  // copy odd numbers to separate array
  Iterator output_end = thrust::copy_if(values.begin(), values.end(), output.begin(), is_odd<int>());

  print_range("output", output.begin(), output_end);

  // another approach is to count the number of values that will
  // be copied, and allocate an array of the right size
  size_t N_odd = thrust::count_if(values.begin(), values.end(), is_odd<int>());

  Vector small_output(N_odd);

  thrust::copy_if(values.begin(), values.end(), small_output.begin(), is_odd<int>());

  print_range("small_output", small_output.begin(), small_output.end());

  // we can also compact sequences with the remove functions, which do the opposite of copy
  Iterator values_end = thrust::remove_if(values.begin(), values.end(), is_odd<int>());

  // since the values after values_end are garbage, we'll resize the vector
  values.resize(values_end - values.begin());

  print_range("values", values.begin(), values.end());

  return 0;
}