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BUG: DatetimeIndex.diff raising TypeError #55761

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Merged
merged 4 commits into from
Oct 31, 2023
Merged

BUG: DatetimeIndex.diff raising TypeError #55761

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0b040a1
BUG: DatetimeIndex.diff raising TypeError
lukemanley Oct 30, 2023
6dcefdc
add test and whatsnew
lukemanley Oct 30, 2023
0894b0c
typing
lukemanley Oct 30, 2023
05b6be3
use Index
lukemanley Oct 31, 2023
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v2.1.3.rst
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Expand Up @@ -13,7 +13,7 @@ including other versions of pandas.

Fixed regressions
~~~~~~~~~~~~~~~~~
-
- Fixed regression in :meth:`DatetimeIndex.diff` raising ``TypeError`` (:issue:`55080`)
-

.. ---------------------------------------------------------------------------
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8 changes: 6 additions & 2 deletions pandas/core/indexes/base.py
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Expand Up @@ -6991,7 +6991,7 @@ def infer_objects(self, copy: bool = True) -> Index:
return result

@final
def diff(self, periods: int = 1) -> Self:
def diff(self, periods: int = 1) -> Index:
"""
Computes the difference between consecutive values in the Index object.

Expand All @@ -7017,7 +7017,11 @@ def diff(self, periods: int = 1) -> Self:
Index([nan, 10.0, 10.0, 10.0, 10.0], dtype='float64')

"""
return self._constructor(self.to_series().diff(periods))
diff = self.to_series().diff(periods)
if diff.dtype != self.dtype:
# e.g. DTI.diff -> TDI
return Index(diff)
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let's just return Index(diff) unconditionally?

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I think we should use self._constructor in order to preserve subclasses as much as possible?

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are there any cases where it makes a difference?

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class MyIndex(Index):
    def _constructor(self):
        return MyIndex

>>> MyIndex([1, 2]).diff(MyIndex([1, 3]))

Wouldn't it be a regression if we didn't return a MyIndex here?

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we dont support 3rd part Index subclasses

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It is noted in the docs that Index subclasses are not supported. @mroeschke, any objections to updating based on that?

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Ah okay I didn't know we didn't support Index subclasses. Fine to update to @jbrockmendel suggestion

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updated to return Index(diff) unconditionally

return self._constructor(diff)

@final
def round(self, decimals: int = 0) -> Self:
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8 changes: 8 additions & 0 deletions pandas/tests/indexes/test_datetimelike.py
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Expand Up @@ -159,3 +159,11 @@ def test_where_cast_str(self, simple_index):

result = index.where(mask, ["foo"])
tm.assert_index_equal(result, expected)

@pytest.mark.parametrize("unit", ["ns", "us", "ms", "s"])
def test_diff(self, unit):
# GH 55080
dti = pd.to_datetime([10, 20, 30], unit=unit).as_unit(unit)
result = dti.diff(1)
expected = pd.TimedeltaIndex([pd.NaT, 10, 10], unit=unit).as_unit(unit)
tm.assert_index_equal(result, expected)