# 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 (GH35439)

- Fixed regression in `Series.truncate()` when trying to truncate a single-element series (GH35544)

- Fixed regression where `DataFrame.to_numpy()` would raise a `RuntimeError` for mixed dtypes when converting to `str` (GH35455)

- Fixed regression where `read_csv()` would raise a `ValueError` when `pandas.options.mode.use_inf_as_na` was set to `True` (GH35493)

- Fixed regression where `pandas.testing.assert_series_equal()` would raise an error when non-numeric dtypes were passed with `check_exact=True` (GH35446)

- Fixed regression in `.groupby(..).rolling(..)` where column selection was ignored (GH35486)

- Fixed regression where `DataFrame.interpolate()` would raise a `TypeError` when the `DataFrame` was empty (GH35598)

- Fixed regression in `DataFrame.shift()` with `axis=1` and heterogeneous dtypes (GH35488)

- Fixed regression in `DataFrame.diff()` with read-only data (GH35559)

- Fixed regression in `.groupby(..).rolling(..)` where a segfault would occur with `center=True` and an odd number of values (GH35552)

- Fixed regression in `DataFrame.apply()` where functions that altered the input in-place only operated on a single row (GH35462)

- Fixed regression in `DataFrame.reset_index()` would raise a `ValueError` on empty `DataFrame` with a `MultiIndex` with a `datetime64` dtype level (GH35606, GH35657)

- Fixed regression where `pandas.merge_asof()` would raise a `UnboundLocalError` when `left_index`, `right_index` and `tolerance` were set (GH35558)

- Fixed regression in `.groupby(..).rolling(..)` where a custom `BaseIndexer` would be ignored (GH35557)

- Fixed regression in `DataFrame.replace()` and `Series.replace()` where compiled regular expressions would be ignored during replacement (GH35680)

- Fixed regression in `aggregate()` where a list of functions would produce the wrong results if at least one of the functions did not aggregate (GH35490)

- Fixed memory usage issue when instantiating large `pandas.arrays.StringArray` (GH35499)

## Bug fixes

- Bug in `Styler` whereby `cell_ids` argument had no effect due to other recent changes (GH35588) (GH35663)

- 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` (GH35715)

- Bug in `to_timedelta()` fails when `arg` is a `Series` with `Int64` dtype containing null values (GH35574)

- Bug in `.groupby(..).rolling(..)` where passing `closed` with column selection would raise a `ValueError` (GH35549)

- Bug in `DataFrame` constructor failing to raise `ValueError` in some cases when `data` and `index` have mismatched lengths (GH33437)

## Contributors

For contributors, please see /usr/share/doc/contributors_list.txt or https://github.com/pandas-dev/pandas/graphs/contributors