BUG: fix combine_first reorders columns #60791
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yuanx749
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mroeschke
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Jan 27, 2025
pandas/core/frame.py
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| @@ -8672,6 +8672,9 @@ def combine( | |||
| """ | |||
| other_idxlen = len(other.index) # save for compare | |||
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| # preserve column order | |||
| new_columns = self.columns.union(other.columns, sort=False) | |||
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Why does this need to be done here as opposed to where it was before?
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I put it before this, other = self.align(other) because align can change the column order of other, as it sorts keys lexicographically.
But I think it is better to do it where it was before, after the early return. I've updated it in the new commit.
mroeschke
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Jan 27, 2025
|
Thanks @yuanx749 |
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I changed an old test for the correct order of columns.
Note that the fix can also be done incombine, if it is preferred to be fixed there, sincecombine_firstcallscombine.With my previous fix, a test in "Future infer strings" failed, which is the corner case when
selfis an empty dataframe. I then made the fix incombine.doc/source/whatsnew/vX.X.X.rstfile if fixing a bug or adding a new feature.