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BUG: DataFrame.__setitem__ raising ValueError when setting multiple values to dup columns #39280

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Merged
merged 2 commits into from
Jan 21, 2021
Merged

BUG: DataFrame.__setitem__ raising ValueError when setting multiple values to dup columns #39280

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4dfd328
BUG: DataFrame.__setitem__ raising ValueError when setting multiple v…
phofl Jan 19, 2021
09a59e0
Fix bug in condition
phofl Jan 19, 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 @@ -275,6 +275,7 @@ Indexing
^^^^^^^^
- Bug in :meth:`CategoricalIndex.get_indexer` failing to raise ``InvalidIndexError`` when non-unique (:issue:`38372`)
- Bug in inserting many new columns into a :class:`DataFrame` causing incorrect subsequent indexing behavior (:issue:`38380`)
- Bug in :meth:`DataFrame.__setitem__` raising ``ValueError`` when setting multiple values to duplicate columns (:issue:`15695`)
- Bug in :meth:`DataFrame.loc`, :meth:`Series.loc`, :meth:`DataFrame.__getitem__` and :meth:`Series.__getitem__` returning incorrect elements for non-monotonic :class:`DatetimeIndex` for string slices (:issue:`33146`)
- Bug in :meth:`DataFrame.reindex` and :meth:`Series.reindex` with timezone aware indexes raising ``TypeError`` for ``method="ffill"`` and ``method="bfill"`` and specified ``tolerance`` (:issue:`38566`)
- Bug in :meth:`DataFrame.__setitem__` raising ``ValueError`` with empty :class:`DataFrame` and specified columns for string indexer and non empty :class:`DataFrame` to set (:issue:`38831`)
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5 changes: 5 additions & 0 deletions pandas/core/frame.py
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Expand Up @@ -3195,6 +3195,11 @@ def __setitem__(self, key, value):
self._setitem_array(key, value)
elif isinstance(value, DataFrame):
self._set_item_frame_value(key, value)
elif is_list_like(value) and 1 < len(
self.columns.get_indexer_for([key])
) == len(value):
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not necessarily for this PR, but it might be worth implementing a Index.count method (mirroring list.count)?

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Yeah this would be helpful probably, something like that would have helped in #39278

# Column to set is duplicated
self._setitem_array([key], value)
else:
# set column
self._set_item(key, value)
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18 changes: 18 additions & 0 deletions pandas/tests/frame/indexing/test_setitem.py
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Expand Up @@ -348,6 +348,24 @@ def test_setitem_frame_length_0_str_key(self, indexer):
expected["A"] = expected["A"].astype("object")
tm.assert_frame_equal(df, expected)

def test_setitem_frame_duplicate_columns(self):
# GH#15695
cols = ["A", "B", "C"] * 2
df = DataFrame(index=range(3), columns=cols)
df.loc[0, "A"] = (0, 3)
df.loc[:, "B"] = (1, 4)
df["C"] = (2, 5)
expected = DataFrame(
[
[0, 1, 2, 3, 4, 5],
[np.nan, 1, 2, np.nan, 4, 5],
[np.nan, 1, 2, np.nan, 4, 5],
],
columns=cols,
dtype="object",
)
tm.assert_frame_equal(df, expected)


class TestDataFrameSetItemWithExpansion:
def test_setitem_listlike_views(self):
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