What's new in 2.2.1 (February XX, 2024)

These are the changes in pandas 2.2.1. See :ref:`release` for a full changelog including other versions of pandas.

Fixed regressions

Fixed memory leak in :func:`read_csv` (:issue:`57039`)
Fixed performance regression in :meth:`Series.combine_first` (:issue:`55845`)
Fixed regression in :func:`merge_ordered` raising TypeError for fill_method="ffill" and how="left" (:issue:`57010`)
Fixed regression in :meth:`DataFrameGroupBy.idxmin`, :meth:`DataFrameGroupBy.idxmax`, :meth:`SeriesGroupBy.idxmin`, :meth:`SeriesGroupBy.idxmax` ignoring the skipna argument (:issue:`57040`)
Fixed regression in :meth:`DataFrameGroupBy.idxmin`, :meth:`DataFrameGroupBy.idxmax`, :meth:`SeriesGroupBy.idxmin`, :meth:`SeriesGroupBy.idxmax` where values containing the minimum or maximum value for the dtype could produce incorrect results (:issue:`57040`)
Fixed regression in :meth:`Index.join` raising TypeError when joining an empty index to a non-empty index containing mixed dtype values (:issue:`57048`)
Fixed regression in :meth:`Series.pct_change` raising a ValueError for an empty :class:`Series` (:issue:`57056`)