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BUG: Enable changing dtype of column where column names are not unique #27256

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BUG: Enable changing dtype of column where column names are not unique #27256

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1 change: 0 additions & 1 deletion pandas/core/indexing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -654,7 +654,6 @@ def can_do_equal_len():
for i, idx in enumerate(indexer)
if i != info_axis
)
and item_labels.is_unique
):
self.obj[item_labels[indexer[info_axis]]] = value
return
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6 changes: 6 additions & 0 deletions pandas/core/internals/managers.py
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Expand Up @@ -1075,6 +1075,12 @@ def value_getitem(placement):
blknos = self._blknos[loc]
blklocs = self._blklocs[loc].copy()

if not self.axes[0].is_unique:
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really don't want to add anything in internals; why is this not possible to be done in pandas/core/indexing?

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@jreback agreed, thanks for feedback! This is work in progress. I'll try to fix it in pandas/core/indexing.

if not isinstance(blknos, np.ndarray):
blknos = [blknos]
if not isinstance(blklocs, np.ndarray):
blklocs = [blklocs]

unfit_mgr_locs = []
unfit_val_locs = []
removed_blknos = []
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11 changes: 11 additions & 0 deletions pandas/tests/indexing/test_iloc.py
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Expand Up @@ -462,6 +462,17 @@ def test_iloc_setitem_dups(self):
df.iloc[[1, 0], [0, 1]] = df.iloc[[1, 0], [0, 1]].reset_index(drop=True)
tm.assert_frame_equal(df, expected)

def test_iloc_change_dtype_dups(self):
# GH 22035 and GH 24798

df = DataFrame([['0', 1, '2']], columns=['A', 'B', 'B'])
df.iloc[:, 0] = df.iloc[:, 0].astype(int)
assert df.dtypes.tolist() == ['int', 'int', 'O']

df = DataFrame([['0', '1', '2']], columns=['A', 'B', 'B'])
df.iloc[:, 0] = df.iloc[:, 0].astype(int)
assert df.dtypes.tolist() == ['int', 'O', 'O']

def test_iloc_getitem_frame(self):
df = DataFrame(
np.random.randn(10, 4), index=range(0, 20, 2), columns=range(0, 8, 2)
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