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BUG: Fix sort_values for empty by argument #40324

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Mar 9, 2021
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BUG: Fix sort_values for empty by argument #40324

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BUG: Fix sort_values for empty by argument
dsaxton Mar 9, 2021
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dsaxton Mar 9, 2021
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dsaxton Mar 9, 2021
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dsaxton Mar 9, 2021
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.3.0.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -437,6 +437,7 @@ Timezones
Numeric
^^^^^^^
- Bug in :meth:`DataFrame.quantile`, :meth:`DataFrame.sort_values` causing incorrect subsequent indexing behavior (:issue:`38351`)
- Bug in :meth:`DataFrame.sort_values` raising an :class:`IndexError` for empty ``by`` (:issue:`40258`)
- Bug in :meth:`DataFrame.select_dtypes` with ``include=np.number`` now retains numeric ``ExtensionDtype`` columns (:issue:`35340`)
- Bug in :meth:`DataFrame.mode` and :meth:`Series.mode` not keeping consistent integer :class:`Index` for empty input (:issue:`33321`)
- Bug in :meth:`DataFrame.rank` with ``np.inf`` and mixture of ``np.nan`` and ``np.inf`` (:issue:`32593`)
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4 changes: 3 additions & 1 deletion pandas/core/frame.py
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Expand Up @@ -5818,7 +5818,7 @@ def sort_values( # type: ignore[override]
keys, orders=ascending, na_position=na_position, key=key
)
indexer = ensure_platform_int(indexer)
else:
elif len(by):

by = by[0]
k = self._get_label_or_level_values(by, axis=axis)
Expand All @@ -5833,6 +5833,8 @@ def sort_values( # type: ignore[override]
indexer = nargsort(
k, kind=kind, ascending=ascending, na_position=na_position, key=key
)
else:
return self.copy()

new_data = self._mgr.take(
indexer, axis=self._get_block_manager_axis(axis), verify=False
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7 changes: 7 additions & 0 deletions pandas/tests/frame/methods/test_sort_values.py
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Expand Up @@ -79,6 +79,13 @@ def test_sort_values(self):
with pytest.raises(ValueError, match=msg):
frame.sort_values(by=["A", "B"], axis=0, ascending=[True] * 5)

def test_sort_values_by_empty_list(self):
# https://github.com/pandas-dev/pandas/issues/40258
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can you add a separate test. also assert that it is not the same frame.

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can you make a completely separate test

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we dont' normally want to mix error checking with other things

expected = DataFrame({"a": [1, 4, 2, 5, 3, 6]})
result = expected.sort_values(by=[])
tm.assert_frame_equal(result, expected)
assert result is not expected

def test_sort_values_inplace(self):
frame = DataFrame(
np.random.randn(4, 4), index=[1, 2, 3, 4], columns=["A", "B", "C", "D"]
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