BUG: Break reference from grouping level to MI #31133
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pandas/core/indexes/multi.py
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| @@ -1235,6 +1235,9 @@ def _set_names(self, names, level=None, validate=True): | |||
| def _get_grouper_for_level(self, mapper, level): | |||
| indexer = self.codes[level] | |||
| level_index = self.levels[level] | |||
| # break references back to ourself so that setting the name | |||
| # on the output of a groupby doesn't reflect back here. | |||
| level_index = level_index.copy() | |||
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you don't need to do this here, rather do it as an else on line 1261 (add it); as take already copies, its just when that condition is not satisfied does it need a copy.
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Fixed, I think. Added a case for Categorical grouper with unobserved categories, so I think all the cases are covered.
Yes, this is just a regression from 0.25.x |
your comments are conflicting, if this is from 0.25.x then we need a note |
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Sorry, I wasn't clear. by "from 0.25.x" I meant "after". This is fixing a regression that's only present on master, not 0.25.x. |
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thanks @TomAugspurger |
…31164) Co-authored-by: Tom Augspurger <[email protected]>
Closes #31068