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#include <thrust/device_vector.h>
#include <thrust/host_vector.h>
#include <thrust/sort.h>
#include <thrust/reduce.h>
#include <thrust/inner_product.h>
#include <thrust/functional.h>
#include <thrust/iterator/zip_iterator.h>
#include <thrust/iterator/constant_iterator.h>
#include <thrust/random.h>
#include <iostream>
#include <iterator>
// This example compute the mode [1] of a set of numbers. If there
// are multiple modes, one with the smallest value it returned.
//
// [1] http://en.wikipedia.org/wiki/Mode_(statistics)
int main(void)
{
const size_t N = 30;
const size_t M = 10;
thrust::default_random_engine rng;
thrust::uniform_int_distribution<int> dist(0, M - 1);
// generate random data on the host
thrust::host_vector<int> h_data(N);
for(size_t i = 0; i < N; i++)
h_data[i] = dist(rng);
// transfer data to device
thrust::device_vector<int> d_data(h_data);
// print the initial data
std::cout << "initial data" << std::endl;
thrust::copy(d_data.begin(), d_data.end(), std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
// sort data to bring equal elements together
thrust::sort(d_data.begin(), d_data.end());
// print the sorted data
std::cout << "sorted data" << std::endl;
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, " "));
std::cout << std::endl;
// find the index of the maximum count
thrust::device_vector<int>::iterator mode_iter;
mode_iter = thrust::max_element(d_output_counts.begin(), d_output_counts.end());
int mode = d_output_keys[mode_iter - d_output_counts.begin()];
int occurances = *mode_iter;
std::cout << "Modal value " << mode << " occurs " << occurances << " times " << std::endl;
return 0;
}
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