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REGR: pivot changing index name of input object #52630

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Merged
merged 1 commit into from
Apr 12, 2023
Merged

REGR: pivot changing index name of input object #52630

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v2.0.1.rst
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Expand Up @@ -17,6 +17,7 @@ Fixed regressions
- Fixed regression in :meth:`Series.describe` showing ``RuntimeWarning`` for extension dtype :class:`Series` with one element (:issue:`52515`)
- Fixed regression in :meth:`DataFrame.sort_values` not resetting index when :class:`DataFrame` is already sorted and ``ignore_index=True`` (:issue:`52553`)
- Fixed regression in :meth:`MultiIndex.isin` raising ``TypeError`` for ``Generator`` (:issue:`52568`)
- Fixed regression in :meth:`DataFrame.pivot` changing :class:`Index` name of input object (:issue:`52629`)

.. ---------------------------------------------------------------------------
.. _whatsnew_201.bug_fixes:
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2 changes: 2 additions & 0 deletions pandas/core/reshape/pivot.py
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Expand Up @@ -519,6 +519,8 @@ def pivot(
# If columns is None we will create a MultiIndex level with None as name
# which might cause duplicated names because None is the default for
# level names
data = data.copy(deep=False)
data.index = data.index.copy()
data.index.names = [
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Is there an opportunity to defer doing this (and avoiding the copy) if we push this to the if/else branches below?

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Both are shallow copies and should take any time compared to the actual pivot op?

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That's fair. Might be a cleanup opportunity in the future but ok as it fixes the regression

name if name is not None else lib.NoDefault for name in data.index.names
]
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7 changes: 7 additions & 0 deletions pandas/tests/reshape/test_pivot.py
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Expand Up @@ -2591,3 +2591,10 @@ def test_pivot_values_is_none(self):
result = df.pivot(columns="b", values=None)
expected = DataFrame(1, index=[0], columns=Index([2], name="b"))
tm.assert_frame_equal(result, expected)

def test_pivot_not_changing_index_name(self):
# GH#52692
df = DataFrame({"one": ["a"], "two": 0, "three": 1})
expected = df.copy(deep=True)
df.pivot(index="one", columns="two", values="three")
tm.assert_frame_equal(df, expected)