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Bug in loc returning multiindex in wrong oder with duplicated indexer #40987

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Merged
merged 6 commits into from
May 26, 2021
Merged

Bug in loc returning multiindex in wrong oder with duplicated indexer #40987

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5473e10
Bug in loc returning multiindex in wrong oder with duplicated indexer
phofl Apr 16, 2021
7738074
Parametrize test
phofl Apr 16, 2021
b27cc24
Merge branch 'master' of https://github.com/pandas-dev/pandas into 40978
phofl May 6, 2021
65665ea
Merge branch 'master' of https://github.com/pandas-dev/pandas into 40978
phofl May 14, 2021
4a60689
Merge branch 'master' of https://github.com/pandas-dev/pandas into 40978
phofl May 23, 2021
7f64bd1
Add second test
phofl May 24, 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 @@ -871,6 +871,7 @@ Indexing
- Bug in :meth:`DataFrame.loc.__setitem__` when setting-with-expansion incorrectly raising when the index in the expanding axis contains duplicates (:issue:`40096`)
- Bug in :meth:`DataFrame.loc` incorrectly matching non-boolean index elements (:issue:`20432`)
- Bug in :meth:`Series.__delitem__` with ``ExtensionDtype`` incorrectly casting to ``ndarray`` (:issue:`40386`)
- Bug in :meth:`DataFrame.loc` returning :class:`MultiIndex` in wrong order if indexer has duplicates (:issue:`40978`)
- Bug in :meth:`DataFrame.__setitem__` raising ``TypeError`` when using a str subclass as the column name with a :class:`DatetimeIndex` (:issue:`37366`)

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1 change: 1 addition & 0 deletions pandas/core/indexes/multi.py
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Expand Up @@ -3446,6 +3446,7 @@ def _reorder_indexer(
new_order = np.arange(n)[indexer]
elif is_list_like(k):
# Generate a map with all level codes as sorted initially
k = algos.unique(k)
key_order_map = np.ones(len(self.levels[i]), dtype=np.uint64) * len(
self.levels[i]
)
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22 changes: 22 additions & 0 deletions pandas/tests/indexing/multiindex/test_loc.py
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Expand Up @@ -764,6 +764,28 @@ def test_loc_getitem_index_differently_ordered_slice_none():
tm.assert_frame_equal(result, expected)


@pytest.mark.parametrize("indexer", [[1, 2, 7, 6, 2, 3, 8, 7], [1, 2, 7, 6, 3, 8]])
def test_loc_getitem_index_differently_ordered_slice_none_duplicates(indexer):
# GH#40978
df = DataFrame(
[1] * 8,
index=MultiIndex.from_tuples(
[(1, 1), (1, 2), (1, 7), (1, 6), (2, 2), (2, 3), (2, 8), (2, 7)]
),
columns=["a"],
)
result = df.loc[(slice(None), indexer), :]
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can you add this as an equivalent test: df_sliced = df.loc[df.index.isin(all_items, level=1), :] should yield the same expected

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Added test, but should not return the same since isin produces an boolean mask, which does not reorder the underlying dataframe. This should be the identity

expected = DataFrame(
[1] * 8,
index=[[1, 1, 2, 1, 2, 1, 2, 2], [1, 2, 2, 7, 7, 6, 3, 8]],
columns=["a"],
)
tm.assert_frame_equal(result, expected)

result = df.loc[df.index.isin(indexer, level=1), :]
tm.assert_frame_equal(result, df)


def test_loc_getitem_drops_levels_for_one_row_dataframe():
# GH#10521
mi = MultiIndex.from_arrays([["x"], ["y"], ["z"]], names=["a", "b", "c"])
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