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BUG: DataFrame.drop fails when columns argument given tuple #43985

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BUG: DataFrame.drop fails when columns argument given tuple #43985

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05de406
check if ndim == 1 and columns=tuple
erfannariman Oct 11, 2021
d1fea9d
add test drop with actual tuple columns
erfannariman Oct 11, 2021
167b315
Merge remote-tracking branch 'upstream/master' into 43978-drop-fails-…
erfannariman Oct 16, 2021
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12 changes: 10 additions & 2 deletions pandas/core/common.py
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Original file line number Diff line number Diff line change
Expand Up @@ -248,7 +248,9 @@ def asarray_tuplesafe(values, dtype: NpDtype | None = None) -> np.ndarray:
return result


def index_labels_to_array(labels, dtype: NpDtype | None = None) -> np.ndarray:
def index_labels_to_array(
labels, dtype: NpDtype | None = None, ndim: int | None = None
) -> np.ndarray:
"""
Transform label or iterable of labels to array, for use in Index.

Expand All @@ -261,9 +263,15 @@ def index_labels_to_array(labels, dtype: NpDtype | None = None) -> np.ndarray:
-------
array
"""
if isinstance(labels, (str, tuple)):
if isinstance(labels, str):
labels = [labels]

if isinstance(labels, tuple):
if ndim == 1:
labels = list(labels)
else:
labels = [labels]

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Would this change behavior for tuple column names?

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Good point, fails indeed, added test for it, will try to resolve.

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Not sure if it is resolvable - if you sometimes treat a tuple as a label and sometimes unpack as a list, seems like there would be unavoidable ambiguities? Would be more inclined to say the behavior is correct as is, but haven't thought about it too much

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I see your point and there probably is some ambiguity since we can also use tuples to drop MultiIndex. I can revert the changes and just add a test that the described case always raises.

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sounds great, thanks!

if not isinstance(labels, (list, np.ndarray)):
try:
labels = list(labels)
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2 changes: 1 addition & 1 deletion pandas/core/indexes/base.py
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Expand Up @@ -6448,7 +6448,7 @@ def drop(self, labels, errors: str_t = "raise") -> Index:
if not isinstance(labels, Index):
# avoid materializing e.g. RangeIndex
arr_dtype = "object" if self.dtype == "object" else None
labels = com.index_labels_to_array(labels, dtype=arr_dtype)
labels = com.index_labels_to_array(labels, dtype=arr_dtype, ndim=self.ndim)

indexer = self.get_indexer_for(labels)
mask = indexer == -1
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14 changes: 14 additions & 0 deletions pandas/tests/frame/methods/test_drop.py
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Expand Up @@ -546,3 +546,17 @@ def test_drop_level_missing_label_multiindex(self):
df = DataFrame(index=MultiIndex.from_product([range(3), range(3)]))
with pytest.raises(KeyError, match="labels \\[5\\] not found in level"):
df.drop(5, level=0)

def test_drop_labels_is_tuple(self):
# GH 43978
df = DataFrame(np.arange(12).reshape(3, 4), columns=["A", "B", "C", "D"])
result = df.drop(columns=("A", "B"))
expected = DataFrame({"C": [2, 6, 10], "D": [3, 7, 11]})
tm.assert_frame_equal(result, expected)

def test_drop_columns_are_tuple(self):
# GH 43978
df = DataFrame(np.arange(6).reshape(3, 2), columns=[("A", "B"), ("C", "D")])
result = df.drop(columns=("A", "B"))
expected = DataFrame([1, 3, 5], columns=[("C", "D")])
tm.assert_frame_equal(result, expected)