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c++vectorcudathrust

Thrust access vector elements by another vector

In Thrust I have three device vectors

device_vector<int> ID(N)
device_vector<float> F(M),Y(N)

where usually M<<N (but that should not matter). All values of ID are in the range 0...M-1.

I would now like to assign Y[i] = F[ID[i]] for all i=0...N-1. If I understood Thrust correctly, I can't do that with for_each and some functor. Is there some way to implement this in a way I can make use of thrust::transform or something similar?

Solution

  • You can do this using thrust:gather, something like:

    device_vector<int> ID(N);
device_vector<float> F(M),Y(N);

thrust::gather(ID.begin(), ID.end(), F.begin(), Y.begin());

    In the call, ID is the map used to gather the values in F and write them into Y.

    [standard disclaimer: written in browser, not tested, use at own risk]