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DOC: Add list of UDF methods to mutation gotcha #39851

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jreback merged 1 commit into from
Feb 16, 2021
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DOC: Add list of UDF methods to mutation gotcha #39851

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4 changes: 3 additions & 1 deletion doc/source/user_guide/gotchas.rst
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Expand Up @@ -183,6 +183,9 @@ testing for membership in the list of column names.
Mutating with User Defined Function (UDF) methods
-------------------------------------------------

This section applies to pandas methods that take a UDF. In particular, the methods
``.apply``, ``.aggregate``, ``.transform``, and ``.filter``.

It is a general rule in programming that one should not mutate a container
while it is being iterated over. Mutation will invalidate the iterator,
causing unexpected behavior. Consider the example:
Expand Down Expand Up @@ -246,7 +249,6 @@ not apply to the container being iterated over.
df = pd.DataFrame({"a": [1, 2, 3], 'b': [4, 5, 6]})
df.apply(f, axis="columns")


``NaN``, Integer ``NA`` values and ``NA`` type promotions
---------------------------------------------------------

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