Hi,
The fact is that you will have a fixed number of samples. You can think of a sample as a NN input. So if you need 2 indices as your data is N_samples,length you can just write the dataset as if you have N_sample x length samples and create a mapping between (N_samples*length ) --> (N_samples,length)
Dataset class is flexible, you just return how many elements you have and it will iterate over that amount. If your data is more complex you just need to think how to code it. I would say that it doesn’t accept several indices as it follow the maxima “1 input - 1 index”