Depending on the op you need to do, you could pack then into a single Tensor with enough info to do your function 

I thought map runs in parallel?

This is not enough to get good performance if the function needs to be applied to each entry I’m afraid.

So Python map doesn’t really work on PyTorch CUDA end?

You can still use it, it’s just that it will call the python function for every element. Which is going to not be optimal