There is a problem in the setup of your reduce_by_key
operation:
new_end = thrust::reduce_by_key(hashKeysVector.begin(),hashKeysVector.end(),hashValueVector.begin(),d_pathId.begin(),d_freqError.begin());
Notice that in the documentation it states:
OutputIterator2 is a model of Output Iterator and and InputIterator2's value_type is convertible to OutputIterator2's value_type.
The value type of your InputIterator2
(i.e. hashValueVector.begin()
) is int
. The value type of your OutputIterator2
is struct hashElem
. Thrust is not going to know how to convert an int
to a struct hashElem
.
Regarding your question, it should not be difficult to capture the return entity from reduce_by_key. According to the documentation it is a thrust pair of two iterators, and these iterators should be consistent with (i.e. of the same vector type and value type) as your keys iterator type and your values iterator type, respectively.
Here's an updated sample based on what you posted, which compiles cleanly:
$ cat t353.cu
#include <iostream>
#include <thrust/device_vector.h>
#include <thrust/pair.h>
#include <thrust/reduce.h>
#include <thrust/sequence.h>
#include <thrust/fill.h>
#include <thrust/copy.h>
typedef thrust::device_vector<int>::iterator dIter;
int main(){
thrust::device_vector<int> hashValueVector(10);
thrust::device_vector<int> hashKeysVector(10);
thrust::device_vector<int> d_pathId(10);
thrust::device_vector<int> d_freqError(10);
thrust::sequence(hashValueVector.begin(), hashValueVector.end());
thrust::fill(hashKeysVector.begin(), hashKeysVector.begin()+5, 1);
thrust::fill(hashKeysVector.begin()+6, hashKeysVector.begin()+10, 2);
thrust::pair<dIter, dIter> new_end;
new_end = thrust::reduce_by_key(hashKeysVector.begin(),hashKeysVector.end(),hashValueVector.begin(),d_pathId.begin(),d_freqError.begin());
std::cout << "Number of results are: " << new_end.first - d_pathId.begin() << std::endl;
thrust::copy(d_pathId.begin(), new_end.first, std::ostream_iterator<int>(std::cout, "\n"));
thrust::copy(d_freqError.begin(), new_end.second, std::ostream_iterator<int>(std::cout, "\n"));
}
$ nvcc -arch=sm_20 -o t353 t353.cu
$ ./t353
Number of results are: 3
1
0
2
10
5
30
$