8000 ENH: try to preserve the dtype on combine_first for the case where the two DataFrame objects have the same columns by danielhrisca · Pull Request #39051 · pandas-dev/pandas · GitHub
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ENH: try to preserve the dtype on combine_first for the case where the two DataFrame objects have the same columns #39051

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Merged
merged 13 commits into from
Jan 15, 2021
Merged

ENH: try to preserve the dtype on combine_first for the case where the two DataFrame objects have the same columns #39051

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0c1d126
ENH: add argument to preserve dtypes of common columns in combine_first
danielhrisca Jan 11, 2021
1a5fe0f
fix black code style
danielhrisca Jan 11, 2021
24f6ffc
fix misspelled word in docstring
danielhrisca Jan 11, 2021
d0f9ed3
update tests and remove preserve_dtypes argument from combine_first
danielhrisca Jan 11, 2021
198eaa4
fix isort and flake8 errors
danielhrisca Jan 11, 2021
f209590
updates according to erview
danielhrisca Jan 12, 2021
5e252d0
update whatsnew with example code
danielhrisca Jan 12, 2021
7c67e3c
wrong header in documentation
danielhrisca Jan 12, 2021
47d0911
fix black code style
danielhrisca Jan 12, 2021
1b5691c
update whatsnew with example code as requested in the review
danielhrisca Jan 13, 2021
ba49f9c
remove redundant check
danielhrisca Jan 13, 2021
a2d4e38
further fix and polish the whatsnew entry
danielhrisca Jan 13, 2021
f937928
fix single letter variable names
danielhrisca Jan 15, 2021
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fix misspelled word in docstring
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danielhrisca committed Jan 11, 2021
commit 24f6ffcff8c750f76288921e48f113f56116d71c
2 changes: 1 addition & 1 deletion pandas/core/frame.py
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Expand Up @@ -6441,7 +6441,7 @@ def combine_first(
Provided DataFrame to use to fill null values.

preserve_dtypes : bool, default False
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we do not want to add a flag for this. simply change it.

Please add some examples for this behaivor

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I was thinking that maybe it is a good idea to keep the current behavior as default, and provide the new behavior as an option

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no its better to just fix this, you can add a whatsnew note in 1.3. everywhere else we cast to common dtypes, this should be no different.

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I'm running into some failed tests that exceed my understand of the lib. Is it expected that if a Series is constructed from a list of None then the result of this combined with some other Series should have the latter's dtype (coercing to the respective NaN value)?

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list of None -> object, so combined -> object

try to preserve the column dtypes afetr combining
try to preserve the column dtypes after combining

.. versionadded:: 1.2.1

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