thrust::count_if

Defined in thrust/count.h

template<typename InputIterator, typename Predicate> thrust::iterator_traits<InputIterator>::difference_type thrust::count_if(InputIterator first, InputIterator last, Predicate pred)

count_if finds the number of elements in [first,last) for which a predicate is true. More precisely, count_if returns the number of iterators i in [first, last) such that pred(*i) == true.

The following code snippet demonstrates how to use count to count the number of odd numbers in a range.

#include <thrust/count.h>
#include <thrust/device_vector.h>
...
struct is_odd
{
  __host__ __device__
  bool operator()(int &x)
  {
    return x & 1;
  }
};
...
// fill a device_vector with even & odd numbers
thrust::device_vector<int> vec(5);
vec[0] = 0;
vec[1] = 1;
vec[2] = 2;
vec[3] = 3;
vec[4] = 4;

// count the odd elements in vec
int result = thrust::count_if(vec.begin(), vec.end(), is_odd());
// result == 2