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# What’s new in 1.1.1 (August 20, 2020)

These are the changes in pandas 1.1.1. See Release notes for a full changelog including other versions of pandas.

## Fixed regressions

- Fixed regression in `CategoricalIndex.format()` where, when stringified scalars had different lengths, the shorter string would be right-filled with spaces, so it had the same length as the longest string (GH 35439)

- Fixed regression in `Series.truncate()` when trying to truncate a single-element series (GH 35544)

- Fixed regression where `DataFrame.to_numpy()` would raise a `RuntimeError` for mixed dtypes when converting to `str` (GH 35455)

- Fixed regression where `read_csv()` would raise a `ValueError` when `pandas.options.mode.use_inf_as_na` was set to `True` (GH 35493)

- Fixed regression where `pandas.testing.assert_series_equal()` would raise an error when non-numeric dtypes were passed with `check_exact=True` (GH 35446)

- Fixed regression in `.groupby(..).rolling(..)` where column selection was ignored (GH 35486)

- Fixed regression where `DataFrame.interpolate()` would raise a `TypeError` when the `DataFrame` was empty (GH 35598)

- Fixed regression in `DataFrame.shift()` with `axis=1` and heterogeneous dtypes (GH 35488)

- Fixed regression in `DataFrame.diff()` with read-only data (GH 35559)

- Fixed regression in `.groupby(..).rolling(..)` where a segfault would occur with `center=True` and an odd number of values (GH 35552)

- Fixed regression in `DataFrame.apply()` where functions that altered the input in-place only operated on a single row (GH 35462)

- Fixed regression in `DataFrame.reset_index()` would raise a `ValueError` on empty `DataFrame` with a `MultiIndex` with a `datetime64` dtype level (GH 35606, GH 35657)

- Fixed regression where `pandas.merge_asof()` would raise a `UnboundLocalError` when `left_index`, `right_index` and `tolerance` were set (GH 35558)

- Fixed regression in `.groupby(..).rolling(..)` where a custom `BaseIndexer` would be ignored (GH 35557)

- Fixed regression in `DataFrame.replace()` and `Series.replace()` where compiled regular expressions would be ignored during replacement (GH 35680)

- Fixed regression in `DataFrameGroupBy.aggregate()` where a list of functions would produce the wrong results if at least one of the functions did not aggregate (GH 35490)

- Fixed memory usage issue when instantiating large `pandas.arrays.StringArray` (GH 35499)

## Bug fixes

- Bug in `Styler` whereby `cell_ids` argument had no effect due to other recent changes (GH 35588) (GH 35663)

- Bug in `pandas.testing.assert_series_equal()` and `pandas.testing.assert_frame_equal()` where extension dtypes were not ignored when `check_dtypes` was set to `False` (GH 35715)

- Bug in `to_timedelta()` fails when `arg` is a `Series` with `Int64` dtype containing null values (GH 35574)

- Bug in `.groupby(..).rolling(..)` where passing `closed` with column selection would raise a `ValueError` (GH 35549)

- Bug in `DataFrame` constructor failing to raise `ValueError` in some cases when `data` and `index` have mismatched lengths (GH 33437)

## Contributors

A total of 20 people contributed patches to this release. People with a “+” by their names contributed a patch for the first time.

- Ali McMaster

- Daniel Saxton

- Eric Goddard +

- Fangchen Li

- Isaac Virshup

- Joris Van den Bossche

- Kevin Sheppard

- Matthew Roeschke

- MeeseeksMachine +

- Pandas Development Team

- Richard Shadrach

- Simon Hawkins

- Terji Petersen

- Tom Augspurger

- Yutaro Ikeda +

- attack68 +

- edwardkong +

- gabicca +

- jbrockmendel

- sanderland +