Manipulate columns on IterableDataset (rename columns, cast, etc.)
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The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_3862). All of your documentation changes will be reflected on that endpoint. > IIUC we check if columns are present/not present directly in the yielded examples and not in info.features because info.features can be None (after map, for instance)?

Yes exactly

> We should develop a solution that ensures info.features is never None. For example, one approach would be to infer them from examples in map and make them promotable from Value("null") to a specific type, in case of None values.

I agree this would be useful. Though inferring the type requires to start streaming some data, which takes a few seconds (compared to being instantaneous right now).

Let's discuss this in a new issue maybe ?
I added:
- add_column
- cast
- rename_column
- rename_columns

related to https://github.com/huggingface/datasets/issues/3444

TODO:
- [x] docs
- [x] tests
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