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ENH: Processing of .mask() for pd.NA #56844 #58730

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v3.0.0.rst
Original file line number Diff line number Diff line change
Expand Up @@ -482,6 +482,7 @@ Other
- Bug in :class:`DataFrame` when passing a ``dict`` with a NA scalar and ``columns`` that would always return ``np.nan`` (:issue:`57205`)
- Bug in :func:`eval` where the names of the :class:`Series` were not preserved when using ``engine="numexpr"``. (:issue:`10239`)
- Bug in :func:`unique` on :class:`Index` not always returning :class:`Index` (:issue:`57043`)
- Bug in :func:`mask` to handle NaN values in condition of function. (:issue:`56844`)
- Bug in :meth:`DataFrame.eval` and :meth:`DataFrame.query` which caused an exception when using NumPy attributes via ``@`` notation, e.g., ``df.eval("@np.floor(a)")``. (:issue:`58041`)
- Bug in :meth:`DataFrame.eval` and :meth:`DataFrame.query` which did not allow to use ``tan`` function. (:issue:`55091`)
- Bug in :meth:`DataFrame.sort_index` when passing ``axis="columns"`` and ``ignore_index=True`` and ``ascending=False`` not returning a :class:`RangeIndex` columns (:issue:`57293`)
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3 changes: 3 additions & 0 deletions pandas/core/generic.py
Original file line number Diff line number Diff line change
Expand Up @@ -9999,6 +9999,9 @@ def mask(
cond = common.apply_if_callable(cond, self)
other = common.apply_if_callable(other, self)

if isinstance(cond, (ABCDataFrame, ABCSeries)):
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Rather than a fillna like this do you see where the logic is breaking down that causes .mask to treat pd.NA the same was as True? We shouldn't have to mess around with pd.NA equality semantics for this fix

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For indexing this goes through check_array_indexer which essentially also converts NA to False (but lower in the stack):

if is_bool_dtype(dtype):
if isinstance(dtype, ExtensionDtype):
indexer = indexer.to_numpy(dtype=bool, na_value=False)

cond = cond.fillna(False)

# see gh-21891
if not hasattr(cond, "__invert__"):
cond = np.array(cond)
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9 changes: 9 additions & 0 deletions pandas/tests/frame/indexing/test_mask.py
Original file line number Diff line number Diff line change
Expand Up @@ -150,3 +150,12 @@ def test_mask_inplace_no_other():
df.mask(cond, inplace=True)
expected = DataFrame({"a": [np.nan, 2], "b": ["x", np.nan]})
tm.assert_frame_equal(df, expected)


def test_mask_with_NA():
df = DataFrame({"A": [0, 1, 2]})
cond = Series([True, False, pd.NA], dtype=pd.BooleanDtype())
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To pass the tests, I think dtype=BooleanDtype() should be used here, and from pandas import BooleanDtype at the top of the file, just like other dtypes.


result = df.mask(cond, other=100)
expected = DataFrame({"A": [100, 1, 2]})
tm.assert_frame_equal(result, expected)
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