BUG: concat(axis=1) sorts by default for DatetimeIndex · Issue #54769 · pandas-dev/pandas (original) (raw)

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Reproducible Example

import pandas as pd

a = pd.Series(1, index=pd.to_datetime(['2000-01-01', '2000-01-03'])) b = pd.Series(2, index=pd.to_datetime(['2000-01-02', '2000-01-04']))

pd.concat([a, b], axis=1)

Issue Description

concat documentation states concat will not sort by default. I believe the default sort behavior was deprecated some time ago. However, there is still a sort=True behavior for DatetimeIndex:

              0    1
2000-01-01  1.0  NaN
2000-01-02  NaN  2.0
2000-01-03  1.0  NaN
2000-01-04  NaN  2.0

The source of this behavior is a hard-coded special-casing in pandas.core.indexes.api.union_indexes. Making this not sort by default seems to break at least one test (test_concat_datetime_timezone) and possibly more.

Expected Behavior

Per the docs, I would expect no sort by default. But that might surprise users if changed. I suppose this either needs to be documented (if intentional) or deprecated (if not intentional).

Installed Versions

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