Features should be updated when `map()` changes schema
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`dataset.column_names` are being updated but `dataset.features` aren't indeed...
2020-07-09T08:52:32Z
https://github.com/huggingface/datasets/issues/342#issuecomment-656000763
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2020-07-09T08:52:32Z
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`dataset.map()` can change the schema and column names.

We should update the features in this case (with what is possible to infer).