attempt to call method 'partial' (a nil value)

I created a hdf5 contains multiple datasets. I'm trying to access some of those with `file:read():partial()`, but it gave me `attempt to call method 'partial' (a nil value)` error.

I think I have installed the correct version of torch-hdf5, since `file:open()` works fine. Any suggestions on how to solve this?

Start by reproducing the error with a multi-dataset HDF5 file and the reported `file:read():partial()` call, then inspect the read API and the behavior of `file:open()`. Done means determining why `partial` is unavailable in this case and either restoring the expected access or documenting the supported usage.

Written by the indexing model from the issue text.