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Preserve freq in TimedeltaIndex subtraction #62214

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Preserve freq in TimedeltaIndex subtraction #62214

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09a4702
Preserve freq in TimedeltaIndex subtraction
Chenghaoxiang Aug 29, 2025
7c642ac
Merge branch 'main' into new-feature
Chenghaoxiang Sep 1, 2025
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6 changes: 6 additions & 0 deletions pandas/core/arrays/datetimelike.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1089,6 +1089,12 @@ def _get_arithmetic_result_freq(self, other) -> BaseOffset | None:
# e.g. TestTimedelta64ArithmeticUnsorted::test_timedelta
# Day is unambiguously 24h
return self.freq
elif (
lib.is_np_dtype(self.dtype, "M")
and isinstance(other, Timestamp)
and isinstance(self.freq, Day)
):
return self.freq

return None

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11 changes: 11 additions & 0 deletions pandas/tests/indexes/datetimes/test_arithmetic.py
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Expand Up @@ -63,3 +63,14 @@ def test_add_dti_day(self):
result = (dti + dti.freq)[:-1]
expected = dti[1:]
tm.assert_index_equal(result, expected)

def test_sub_timestamp_preserves_day_freq(self):
# GH#62094
dti = date_range("2021-01-01", periods=5, freq="D")
ts = Timestamp("2020-01-01")

result = dti - ts

# The one crucial assertion:
assert isinstance(result, TimedeltaIndex)
assert result.freq == dti.freq
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