pandas (original) (raw)

Feature Type

Adding new functionality to pandas
Changing existing functionality in pandas
Removing existing functionality in pandas

Problem Description

For a very long time now it used to be the default behaviour that calling pd.concat(..., axis=1) on DataFrames with DateTimeIndex would result in a DataFrame with sorted index. This is very reasonable default behaviour and pretty much what one wants in this case the vast majority of times.

With #54769 this was considered a bug simply because it wasn't documented correctly, and now the default behaviour, without any warning, was suddenly changed. This means likely code breakages across many users' libraries that were written based on the (up until now true) assumption that concatenating timeseries-like DataFrames/Series would give another timeseries-like object, i.e. something with a clearly sorted DateTimeIndex. Making sort=False work in the DateTimeIndex case is of course something that should be ensured, as it is something that might come in handy in some rare cases, but having that the default I don't think is a good idea at all, given the opposite has been the default for a long time and frankly makes more sense.

Feature Description

Change the default back to sort=True in the case of DataFrames/Series with DateTimeIndex and update the documentation to more accurately reflect this original default behaviour.

Alternative Solutions

Many users suddenly (and without clear warning) need to put sort=True in all the places they call pd.concat on timeseries-like Pandas objects.

Additional Context

No response