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BUG: Fix bug in loc setitem changing the dtype when condition is False #37672

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Merged
merged 30 commits into from
Dec 13, 2021
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BUG: Fix bug in loc setitem changing the dtype when condition is False #37672

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9df9c89
Fix bug in setitem when indexer was only false changed dtype
phofl Nov 3, 2020
6e0ec24
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Nov 6, 2020
26b7dae
Add space
phofl Nov 6, 2020
11d27b1
Move condition to elif
phofl Nov 8, 2020
a527342
Move test
phofl Nov 8, 2020
722cf9d
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Nov 9, 2020
345b3c1
Adjust test
phofl Nov 9, 2020
8c57c09
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Nov 10, 2020
3b92d31
Fix whatsnew
phofl Nov 14, 2020
97203de
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Nov 14, 2020
2f7bf13
Make test more clear
phofl Nov 14, 2020
eb3b204
Use asarray
phofl Nov 15, 2020
9d59de4
Parametrize test
phofl Nov 16, 2020
b02e629
Move if condition
phofl Nov 17, 2020
b27c825
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Nov 17, 2020
8edc7d0
Remove import
phofl Nov 17, 2020
e57e407
Rename parametrization
phofl Nov 17, 2020
6506df5
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Nov 17, 2020
8cdef72
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Dec 21, 2020
c14d7b2
Move whatsnew
phofl Dec 21, 2020
01d7ffc
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Jan 21, 2021
da94459
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl Apr 17, 2021
85120c9
Fix dep warning
phofl Apr 17, 2021
bae602e
Fix corner case
phofl Apr 17, 2021
824c927
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl May 14, 2021
6871ae9
Merge branch 'master' of https://github.com/pandas-dev/pandas into 37550
phofl May 23, 2021
56f4f76
Merge remote-tracking branch 'upstream/master' into 37550
phofl Dec 10, 2021
d334c7a
Move check
phofl Dec 10, 2021
f12ef06
Split tests
phofl Dec 10, 2021
131d168
Merge remote-tracking branch 'upstream/master' into 37550
phofl Dec 10, 2021
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.2.0.rst
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Expand Up @@ -525,6 +525,7 @@ Indexing
- Bug in :meth:`DataFrame.loc` returned requested key plus missing values when ``loc`` was applied to single level from :class:`MultiIndex` (:issue:`27104`)
- Bug in indexing on a :class:`Series` or :class:`DataFrame` with a :class:`CategoricalIndex` using a listlike indexer containing NA values (:issue:`37722`)
- Bug in :meth:`DataFrame.xs` ignored ``droplevel=False`` for columns (:issue:`19056`)
- Bug in :meth:`DataFrame.loc.__setitem__` changing dtype when indexer was completely ``False`` (:issue:`37550`)

Missing
^^^^^^^
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5 changes: 3 additions & 2 deletions pandas/core/internals/blocks.py
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Expand Up @@ -928,10 +928,11 @@ def setitem(self, indexer, value):

elif lib.is_scalar(value) and not isna(value):
dtype, _ = infer_dtype_from_scalar(value, pandas_dtype=True)

elif is_list_like(value) and is_empty_indexer(indexer, np.array(value)):
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any way to avoid the np.array call? i think that makes a copy if we have eg a list

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@phofl phofl Nov 8, 2020 •
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I don't think so, is_empty_indexer requires an ndarray, while value may be a list.

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the test is for loc.__setitem__. is that (or i guess iloc.__setitem__) the only way we can get here? it may make sense to do this in setitem_with_indexer

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Yeah, that would be possible I think.
Sport would be in

pandas/pandas/core/indexing.py

Line 1567 in 524fc9c

for i, idx in enumerate(indexer):

Ran the tests in indexing, frame/indexing and series/indexing locally, this seems to work. Let me know, if we should move this

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you can use np.asarray, also can we check len of the indexer here first to short-cut?

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Thx used asarray. Indexer is a tuple containing an empty list, len does not work here unfortunately.

return self
else:
# e.g. we are bool dtype and value is nan
# TODO: watch out for case with listlike value and scalar/empty indexer
# TODO: watch out for case with listlike value and scalar indexer
dtype, _ = maybe_promote(np.array(value).dtype)
return self.astype(dtype).setitem(indexer, value)

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11 changes: 11 additions & 0 deletions pandas/tests/frame/indexing/test_setitem.py
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Expand Up @@ -339,3 +339,14 @@ def test_setitem_boolean_mask(self, mask_type, float_frame):
expected = df.copy()
expected.values[np.array(mask)] = np.nan
tm.assert_frame_equal(result, expected)

def test_setitem_loc_only_false_indexer_dtype_changed(self):
# GH#37550
# Dtype is only changed when value to set is a Series
df = DataFrame({"a": ["a"], "b": [1], "c": [1]})
df.loc[[False], ["b"]] = 10 - df["c"]
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can you make clear either in the test name and/or comment that/whether the type of indexer for ["b"] is relevant

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Added comment and parametrized test

expected = DataFrame({"a": ["a"], "b": [1], "c": [1]})
tm.assert_frame_equal(df, expected)

df.loc[[False], ["b"]] = 10 - 1
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you can simplify to 9

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Thx

tm.assert_frame_equal(df, expected)