ENH: Add left_semi merge #62961
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ENH: Add left_semi merge #62961
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Dr-Irv reviewed Nov 2, 2025
pandas/core/frame.py Outdated
Comment on lines 339 to 342
| * inner: use intersection of keys from both frames, similar to a SQL inner | ||
| join; preserve the order of the left keys. | ||
| * left_semi: Filter for rows in the left that have a match on the right; | ||
| preserve the order of the left keys. |
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These sound really similar. I think the difference is that if a key appears more than once on the left, then only one match is returned. Secondly, no columns from the right are returned. Did I get that right? If so, I think you may want to say more here.
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This is modeled after what a database semi join does. I can refer to that but I really don’t want to get too deep into the semantics here since there is a standard out there that defines this
Dr-Irv requested changes Nov 2, 2025
Dr-Irv approved these changes Nov 3, 2025
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doc/source/whatsnew/vX.X.X.rstfile if fixing a bug or adding a new feature.Reviving an old PR of mine