 #include <thrust/host_vector.h>
 #include <thrust/sort.h>
 #include <thrust/reduce.h>
+#include <thrust/functional.h>
 #include <thrust/iterator/zip_iterator.h>
 #include <thrust/iterator/constant_iterator.h>
 


int main(void)
{
    const size_t N = 3000;
    const size_t M = 10;

    // generate random data on the host

    thrust::copy(d_data.begin(), d_data.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << std::endl;

    // count number of unique keys
    size_t num_unique = thrust::inner_product(d_data.begin(), d_data.end() - 1,
                                              d_data.begin() + 1,
                                              0,
                                              thrust::plus<int>(),
                                              thrust::not_equal_to<int>()) + 1;

    // count multiplicity of each key
    thrust::device_vector<int> d_output_keys(num_unique);
    thrust::device_vector<int> d_output_counts(num_unique);
    thrust::reduce_by_key(d_data.begin(), d_data.end(),
                          thrust::constant_iterator<int>(1),
                          d_output_keys.begin(),
                          d_output_counts.begin());
    
    // print the counts
    std::cout << "values" << std::endl;
    thrust::copy(d_output_keys.begin(), d_output_keys.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << std::endl;

    // print the counts
    std::cout << "counts" << std::endl;
    thrust::copy(d_output_counts.begin(), d_output_counts.end(), std::ostream_iterator<int>(std::cout, " "));
