Does datasets support nested datasets? I have a nested dataset path dict, e.g.,
{
	a: {
		train:
		dev:
		test:
	},
	b: {
		train:
		dev:
		test:
	}
}

and load_dataset seems unhappy with this structure (TypeError: expected str, bytes or os.PathLike object, not dict). Does that imply I have to do load_dataset for each sub-dataset and then merge them together?
Further, is there any support for over/undersampling given multiple (sub-)datasets? Thanks a lot!