concatenate_datasets for iterable datasets

[lhoestq]

Currently concatenate_datasets only works for map-style Dataset.

It would be nice to have it work for IterableDataset objects as well.

It would simply chain the iterables of the iterable datasets.

[KennethEnevoldsen]

It is probably worth noting here that the documentation is misleading (indicating that it does work for IterableDatasets):

You can also mix several datasets together by taking alternating examples from each one to create a new dataset. This is known as interleaving, and you can use it with interleave_datasets(). Both interleave_datasets() and concatenate_datasets() will work with regular Dataset and IterableDataset objects. Refer to the Stream section for an example of how it’s used.

[lhoestq]

Thanks for the heads up, I'll fix that