Sorting a structure of arrays using Thrust - sorting

Question

I am working on CUDA and facing the following problem.
I have a following structure of arrays:
typedef struct Edge{
int *from, *to, *weight;
}
I want to sort this structure on weight array such that the corresponding "from" and "to" arrays get updated too. I thought of using Thrust library but it works only on vectors is what I understood. I can sort_by_key and get two arrays sorted but I am not able to understand how to sort three arrays? I even looked at zip_iterator but did not understand how to use it to serve my purpose. Please help

Answer 1

First decouple the structure into 1) keys, and 2) paddings. Then sort the keys and reorder paddings accordingly. For example, break this structure:
typedef struct Edge{
int from, to, weight;
}
into:
int weight[N];
typedef struct Edge{
int from, to;
}
The full code is here:
#include <thrust/device_vector.h>
#include <thrust/host_vector.h>
#include <cmath>
#include <thrust/sort.h>
typedef struct pad {
int from;
int to;
} padd;
__host__ padd randPad() {
padd p;
p.from = rand();
p.to = rand();
return p;
}
__host__ std::ostream& operator<< (std::ostream& os, const padd& p) {
os << "(" << p.to << " , " << p.from << " )";
return os;
}
int main(void)
{
// allocation
#define N 4
thrust::host_vector<int> h_keys(4);
thrust::host_vector<padd> h_pad(4);
// initilization
thrust::generate(h_keys.begin(), h_keys.end(), rand);
thrust::generate(h_pad.begin(), h_pad.end(), randPad);
// print unsorted data
std::cout<<"Unsorted keys\n";
thrust::copy(h_keys.begin(), h_keys.end(), std::ostream_iterator<int>(std::cout, "\n"));
std::cout<<"\nUnsorted paddings\n";
thrust::copy(h_pad.begin(), h_pad.end(), std::ostream_iterator<padd>(std::cout, "\n"));
// transfer to device
thrust::device_vector<int> d_keys = h_keys;
thrust::device_vector<padd> d_pad = h_pad;
//thrust::sort(d_keys.begin(), d_keys.end());
// sort
thrust::sort_by_key(d_keys.begin(), d_keys.end(), d_pad.begin());
// transfer back to host
thrust::copy(d_keys.begin(), d_keys.end(), h_keys.begin());
thrust::copy(d_pad.begin(), d_pad.end(), h_pad.begin());
// print the results
std::cout<<"\nSorted keys\n";
thrust::copy(h_keys.begin(), h_keys.end(), std::ostream_iterator<int>(std::cout, "\n"));
std::cout<<"\nSorted paddings\n";
thrust::copy(h_pad.begin(), h_pad.end(), std::ostream_iterator<padd>(std::cout, "\n"));
return 0;
}
The output would be something like this:
Unsorted keys
1804289383
846930886
1681692777
1714636915
Unsorted paddings
(424238335 , 1957747793 )
(1649760492 , 719885386 )
(1189641421 , 596516649 )
(1350490027 , 1025202362 )
Sorted keys
846930886
1681692777
1714636915
1804289383
Sorted paddings
(1649760492 , 719885386 )
(1189641421 , 596516649 )
(1350490027 , 1025202362 )
(424238335 , 1957747793 )