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BUG: Series[sparse].where losing fill_value #45691

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Merged
merged 3 commits into from
Jan 29, 2022
Merged

BUG: Series[sparse].where losing fill_value #45691

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3d74aef
BUG: Series[sparse].where losing fill_value
jbrockmendel Jan 29, 2022
bef5e98
GH refs
jbrockmendel Jan 29, 2022
7095a50
typo fixup
jbrockmendel Jan 29, 2022
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v1.5.0.rst
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Expand Up @@ -316,7 +316,7 @@ Reshaping

Sparse
^^^^^^
-
- Bug in :meth:`Series.where` and :meth:`DataFrame.where` with ``SparseDtype`` failing to retain the array's ``fill_value`` (:issue:`45691`)
-

ExtensionArray
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3 changes: 2 additions & 1 deletion pandas/core/arrays/sparse/array.py
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Expand Up @@ -1355,7 +1355,8 @@ def _where(self, mask, value):
# NB: may not preserve dtype, e.g. result may be Sparse[float64]
# while self is Sparse[int64]
naive_implementation = np.where(mask, self, value)
result = type(self)._from_sequence(naive_implementation)
dtype = SparseDtype(naive_implementation.dtype, fill_value=self.fill_value)
result = type(self)._from_sequence(naive_implementation, dtype=dtype)
return result

# ------------------------------------------------------------------------
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14 changes: 14 additions & 0 deletions pandas/tests/arrays/sparse/test_array.py
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Expand Up @@ -880,6 +880,20 @@ def test_generator_warnings(self):
pass
assert len(w) == 0

def test_where_retain_fill_value(self):
# GH#45691 don't lose fill_value on _where
arr = SparseArray([np.nan, 1.0], fill_value=0)

mask = np.array([True, False])

res = arr._where(~mask, 1)
exp = SparseArray([1, 1.0], fill_value=0)
tm.assert_sp_array_equal(res, exp)

ser = pd.Series(arr)
res = ser.where(~mask, 1)
tm.assert_series_equal(res, pd.Series(exp))

def test_fillna(self):
s = SparseArray([1, np.nan, np.nan, 3, np.nan])
res = s.fillna(-1)
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