issue_comments: 794116358

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https://github.com/pydata/xarray/pull/3925#issuecomment-794116358 https://api.github.com/repos/pydata/xarray/issues/3925 794116358 MDEyOklzc3VlQ29tbWVudDc5NDExNjM1OA== 4160723 2021-03-09T16:23:17Z 2021-03-09T16:23:17Z MEMBER

pandas is 1000x faster than NumPy if the index is pre-existing, but 100x slower if the index is new. That's a 1e5 fold slow-down!

I think users will appreciate the flexibility, but if there's some way we warn users that they really should set the index ahead of time when they are doing repeating indexing that could also be welcome.

I think it's a good use case for some kind of EphemeralIndex (or BasicIndex or NumpyIndex) once the explicit index refactoring is done, along with some good documentation on which index to choose for which purpose.

 
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