DOC: prettify bug fixes section (#15846)

Author: jreback

doc/source/whatsnew/v0.20.0.txt

@@ -913,147 +913,141 @@ Performance Improvements
 Bug Fixes
 ~~~~~~~~~
 
+Conversion
+^^^^^^^^^^
+
 - Bug in ``Timestamp.replace`` now raises ``TypeError`` when incorrect argument names are given; previously this raised ``ValueError`` (:issue:`15240`)
+- Bug in ``Timestamp.replace`` with compat for passing long integers (:issue:`15030`)
 - Bug in ``Timestamp`` returning UTC based time/date attributes when a timezone was provided (:issue:`13303`)
-- Bug in ``Index`` power operations with reversed operands (:issue:`14973`)
 - Bug in ``TimedeltaIndex`` addition where overflow was being allowed without error (:issue:`14816`)
 - Bug in ``TimedeltaIndex`` raising a ``ValueError`` when boolean indexing with ``loc`` (:issue:`14946`)
+- Bug in catching an overflow in ``Timestamp`` + ``Timedelta/Offset`` operations (:issue:`15126`)
 - Bug in ``DatetimeIndex.round()`` and ``Timestamp.round()`` floating point accuracy when rounding by milliseconds or less (:issue:`14440`, :issue:`15578`)
 - Bug in ``astype()`` where ``inf`` values were incorrectly converted to integers. Now raises error now with ``astype()`` for Series and DataFrames (:issue:`14265`)
 - Bug in ``DataFrame(..).apply(to_numeric)`` when values are of type decimal.Decimal. (:issue:`14827`)
 - Bug in ``describe()`` when passing a numpy array which does not contain the median to the ``percentiles`` keyword argument (:issue:`14908`)
-- Bug in ``DataFrame.sort_values()`` when sorting by multiple columns where one column is of type ``int64`` and contains ``NaT`` (:issue:`14922`)
-- Bug in ``DataFrame.reindex()`` in which ``method`` was ignored when passing ``columns`` (:issue:`14992`)
-- Bug in ``pd.to_numeric()`` in which float and unsigned integer elements were being improperly casted (:issue:`14941`, :issue:`15005`)
 - Cleaned up ``PeriodIndex`` constructor, including raising on floats more consistently (:issue:`13277`)
-- Bug in ``pd.read_csv()`` in which the ``dialect`` parameter was not being verified before processing (:issue:`14898`)
-- Bug in ``pd.read_fwf()`` where the skiprows parameter was not being respected during column width inference (:issue:`11256`)
-- Bug in ``pd.read_csv()`` in which missing data was being improperly handled with ``usecols`` (:issue:`6710`)
-- Bug in ``pd.read_csv()`` in which a file containing a row with many columns followed by rows with fewer columns would cause a crash (:issue:`14125`)
-- Added checks in ``pd.read_csv()`` ensuring that values for ``nrows`` and ``chunksize`` are valid (:issue:`15767`)
-- Bug in ``pd.tools.hashing.hash_pandas_object()`` in which hashing of categoricals depended on the ordering of categories, instead of just their values. (:issue:`15143`)
-- Bug in ``.groupby(..).resample()`` when passed the ``on=`` kwarg. (:issue:`15021`)
 - Bug in using ``__deepcopy__`` on empty NDFrame objects (:issue:`15370`)
-- Bug in ``DataFrame.loc`` with indexing a ``MultiIndex`` with a ``Series`` indexer (:issue:`14730`, :issue:`15424`)
-- Bug in ``DataFrame.loc`` with indexing a ``MultiIndex`` with a numpy array (:issue:`15434`)
-- Bug in ``Rolling.quantile`` function that caused a segmentation fault when called with a quantile value outside of the range [0, 1] (:issue:`15463`)
-- Bug in ``pd.cut()`` with a single bin on an all 0s array (:issue:`15428`)
-- Bug in ``pd.qcut()`` with a single quantile and an array with identical values (:issue:`15431`)
-- Compat with SciPy 0.19.0 for testing on ``.interpolate()`` (:issue:`15662`)
-- Bug in ``Series.asof`` which raised if the series contained all ``np.nan`` (:issue:`15713`)
-
-- Compat for 32-bit platforms for ``.qcut/cut``; bins will now be ``int64`` dtype (:issue:`14866`)
-
-- Properly set ``__name__`` and ``__qualname__`` for ``Groupby.*`` functions (:issue:`14620`)
-- Bug in ``.at`` when selecting from a tz-aware column (:issue:`15822`)
-- Bug in the display of ``.info()`` where a qualifier (+) would always be displayed with a ``MultiIndex`` that contains only non-strings (:issue:`15245`)
 - Bug in ``.replace()`` may result in incorrect dtypes. (:issue:`12747`, :issue:`15765`)
 - Bug in ``Series.replace`` and ``DataFrame.replace`` which failed on empty replacement dicts (:issue:`15289`)
 - Bug in ``Series.replace`` which replaced a numeric by string (:issue:`15743`)
-
+- Bug in ``Index`` construction with ``NaN`` elements and integer dtype specified (:issue:`15187`)
+- Bug in ``Series`` construction with a datetimetz (:issue:`14928`)
+- Bug in ``Series.dt.round()`` inconsistent behaviour on ``NaT`` 's with different arguments (:issue:`14940`)
+- Bug in ``Series`` constructor when both ``copy=True`` and ``dtype`` arguments are provided (:issue:`15125`)
+- Incorrect dtyped ``Series`` was returned by comparison methods (e.g., ``lt``, ``gt``, ...) against a constant for an empty ``DataFrame`` (:issue:`15077`)
+- Bug in ``Series.ffill()`` with mixed dtypes containing tz-aware datetimes. (:issue:`14956`)
+- Bug in ``DataFrame.fillna()`` where the argument ``downcast`` was ignored when fillna value was of type ``dict`` (:issue:`15277`)
 - Bug in ``.asfreq()``, where frequency was not set for empty ``Series`` (:issue:`14320`)
 
-- Bug in ``pd.read_msgpack()`` in which ``Series`` categoricals were being improperly processed (:issue:`14901`)
-- Bug in ``Series.ffill()`` with mixed dtypes containing tz-aware datetimes. (:issue:`14956`)
-- Bug in interactions with ``Qt`` when a ``QtApplication`` already exists (:issue:`14372`)
-- Bug in ``DataFrame.isin`` comparing datetimelike to empty frame (:issue:`15473`)
+Indexing
+^^^^^^^^
 
+- Bug in ``Index`` power operations with reversed operands (:issue:`14973`)
+- Bug in ``DataFrame.sort_values()`` when sorting by multiple columns where one column is of type ``int64`` and contains ``NaT`` (:issue:`14922`)
+- Bug in ``DataFrame.reindex()`` in which ``method`` was ignored when passing ``columns`` (:issue:`14992`)
+- Bug in ``DataFrame.loc`` with indexing a ``MultiIndex`` with a ``Series`` indexer (:issue:`14730`, :issue:`15424`)
+- Bug in ``DataFrame.loc`` with indexing a ``MultiIndex`` with a numpy array (:issue:`15434`)
+- Bug in ``Series.asof`` which raised if the series contained all ``np.nan`` (:issue:`15713`)
+- Bug in ``.at`` when selecting from a tz-aware column (:issue:`15822`)
 - Bug in ``Series.where()`` and ``DataFrame.where()`` where array-like conditionals were being rejected (:issue:`15414`)
 - Bug in ``Series.where()`` where TZ-aware data was converted to float representation (:issue:`15701`)
-- Bug in ``Index`` construction with ``NaN`` elements and integer dtype specified (:issue:`15187`)
-- Bug in ``Series`` construction with a datetimetz (:issue:`14928`)
+- Bug in ``.loc`` that would not return the correct dtype for scalar access for a DataFrame (:issue:`11617`)
 - Bug in output formatting of a ``MultiIndex`` when names are integers (:issue:`12223`, :issue:`15262`)
+- Bug in ``Categorical.searchsorted()`` where alphabetical instead of the provided categorical order was used (:issue:`14522`)
+- Bug in ``Series.iloc`` where a ``Categorical`` object for list-like indexes input was returned, where a ``Series`` was expected. (:issue:`14580`)
+- Bug in ``DataFrame.isin`` comparing datetimelike to empty frame (:issue:`15473`)
+- Bug in ``.reset_index()`` when an all ``NaN`` level of a ``MultiIndex`` would fail (:issue:`6322`)
+- Bug in creating a ``MultiIndex`` with tuples and not passing a list of names; this will now raise ``ValueError`` (:issue:`15110`)
+- Bug in the HTML display with with a ``MultiIndex`` and truncation (:issue:`14882`)
+- Bug in the display of ``.info()`` where a qualifier (+) would always be displayed with a ``MultiIndex`` that contains only non-strings (:issue:`15245`)
 
-- Bug in compat for passing long integers to ``Timestamp.replace`` (:issue:`15030`)
-- Bug in ``.loc`` that would not return the correct dtype for scalar access for a DataFrame (:issue:`11617`)
-- Bug in ``GroupBy.get_group()`` failing with a categorical grouper (:issue:`15155`)
-- Bug in ``pandas.tools.utils.cartesian_product()`` with large input can cause overflow on windows (:issue:`15265`)
+I/O
+^^^
 
+- Bug in ``pd.to_numeric()`` in which float and unsigned integer elements were being improperly casted (:issue:`14941`, :issue:`15005`)
+- Bug in ``pd.read_fwf()`` where the skiprows parameter was not being respected during column width inference (:issue:`11256`)
+- Bug in ``pd.read_csv()`` in which the ``dialect`` parameter was not being verified before processing (:issue:`14898`)
+- Bug in ``pd.read_csv()`` in which missing data was being improperly handled with ``usecols`` (:issue:`6710`)
+- Bug in ``pd.read_csv()`` in which a file containing a row with many columns followed by rows with fewer columns would cause a crash (:issue:`14125`)
+- Bug in ``pd.read_csv()`` for the C engine where ``usecols`` were being indexed incorrectly with ``parse_dates`` (:issue:`14792`)
+- Bug in ``pd.read_csv()`` with ``parse_dates`` when multiline headers are specified (:issue:`15376`)
+- Bug in ``pd.read_csv()`` with ``float_precision='round_trip'`` which caused a segfault when a text entry is parsed (:issue:`15140`)
+- Added checks in ``pd.read_csv()`` ensuring that values for ``nrows`` and ``chunksize`` are valid (:issue:`15767`)
+- Bug in ``pd.tools.hashing.hash_pandas_object()`` in which hashing of categoricals depended on the ordering of categories, instead of just their values. (:issue:`15143`)
+- Bug in ``.to_json()`` where ``lines=True`` and contents (keys or values) contain escaped characters (:issue:`15096`)
+- Bug in ``.to_json()`` causing single byte ascii characters to be expanded to four byte unicode (:issue:`15344`)
+- Bug in ``.read_json()`` for Python 2 where ``lines=True`` and contents contain non-ascii unicode characters (:issue:`15132`)
+- Bug in ``pd.read_msgpack()`` in which ``Series`` categoricals were being improperly processed (:issue:`14901`)
+- Bug in ``pd.read_msgpack()`` which did not allow loading of a dataframe with an index of type ``CategoricalIndex`` (:issue:`15487`)
+- Bug in ``pd.read_msgpack()`` when deserializing a ``CategoricalIndex`` (:issue:`15487`)
 - Bug in ``DataFrame.to_records()`` with converting a ``DatetimeIndex`` with a timezone (:issue:`13937`)
+- Bug in ``DataFrame.to_records()`` which failed with unicode characters in column names (:issue:`11879`)
+- Bug in ``.to_sql()`` when writing a DataFrame with numeric index names (:issue:`15404`).
+- Bug in ``DataFrame.to_html()`` with ``index=False`` and ``max_rows`` raising in ``IndexError`` (:issue:`14998`)
+- Bug in ``pd.read_hdf()`` passing a ``Timestamp`` to the ``where`` parameter with a non date column (:issue:`15492`)
+- Bug in ``DataFrame.to_stata()`` and ``StataWriter`` which produces incorrectly formatted files to be produced for some locales (:issue:`13856`)
+- Bug in ``StataReader`` and ``StataWriter`` which allows invalid encodings (:issue:`15723`)
 
+Plotting
+^^^^^^^^
 
-- Bug in ``.groupby(...).rolling(...)`` when ``on`` is specified and using a ``DatetimeIndex`` (:issue:`15130`)
-
-
-- Bug in ``to_sql`` when writing a DataFrame with numeric index names (:issue:`15404`).
-- Bug in ``Series.iloc`` where a ``Categorical`` object for list-like indexes input was returned, where a ``Series`` was expected. (:issue:`14580`)
-- Bug in repr-formatting a ``SparseDataFrame`` after a value was set on (a copy of) one of its series (:issue:`15488`)
-- Bug in ``SparseSeries.reindex`` on single level with list of length 1 (:issue:`15447`)
+- Bug in ``DataFrame.hist`` where ``plt.tight_layout`` caused an ``AttributeError``  (use ``matplotlib >= 2.0.1``) (:issue:`9351`)
+- Bug in ``DataFrame.boxplot`` where ``fontsize`` was not applied to the tick labels on both axes (:issue:`15108`)
 
+Groupby/Resample/Rolling
+^^^^^^^^^^^^^^^^^^^^^^^^
 
+- Bug in ``.groupby(..).resample()`` when passed the ``on=`` kwarg. (:issue:`15021`)
+- Properly set ``__name__`` and ``__qualname__`` for ``Groupby.*`` functions (:issue:`14620`)
+- Bug in ``GroupBy.get_group()`` failing with a categorical grouper (:issue:`15155`)
+- Bug in ``.groupby(...).rolling(...)`` when ``on`` is specified and using a ``DatetimeIndex`` (:issue:`15130`)
 - Bug in groupby operations with timedelta64 when passing ``numeric_only=False`` (:issue:`5724`)
 - Bug in ``groupby.apply()`` coercing ``object`` dtypes to numeric types, when not all values were numeric (:issue:`14423`, :issue:`15421`, :issue:`15670`)
-
-
-- Bug in ``DataFrame.to_html`` with ``index=False`` and ``max_rows`` raising in ``IndexError`` (:issue:`14998`)
-
-- Bug in ``Categorical.searchsorted()`` where alphabetical instead of the provided categorical order was used (:issue:`14522`)
-
-
-
-- Bug in ``resample``, where a non-string ```loffset`` argument would not be applied when resampling a timeseries (:issue:`13218`)
-
-
-
-- Bug in ``.rank()`` which incorrectly ranks ordered categories (:issue:`15420`)
-- Bug in ``.corr()`` and ``.cov()`` where the column and index were the same object (:issue:`14617`)
-
-
-- Require at least 0.23 version of cython to avoid problems with character encodings (:issue:`14699`)
-- Bug in ``pd.pivot_table()`` where no error was raised when values argument was not in the columns (:issue:`14938`)
-
-- Bug in ``.to_json()`` where ``lines=True`` and contents (keys or values) contain escaped characters (:issue:`15096`)
-- Bug in ``.to_json()`` causing single byte ascii characters to be expanded to four byte unicode (:issue:`15344`)
-- Bug in ``.read_json()`` for Python 2 where ``lines=True`` and contents contain non-ascii unicode characters (:issue:`15132`)
+- Bug in ``resample``, where a non-string ``loffset`` argument would not be applied when resampling a timeseries (:issue:`13218`)
+- Bug in ``DataFrame.groupby().describe()`` when grouping on ``Index`` containing tuples (:issue:`14848`)
+- Bug in ``groupby().nunique()`` with a datetimelike-grouper where bins counts were incorrect (:issue:`13453`)
+- Bug in ``groupby.transform()`` that would coerce the resultant dtypes back to the original (:issue:`10972`, :issue:`11444`)
+- Bug in ``groupby.agg()`` incorrectly localizing timezone on ``datetime`` (:issue:`15426`, :issue:`10668`, :issue:`13046`)
 - Bug in ``.rolling/expanding()`` functions where ``count()`` was not counting ``np.Inf``, nor handling ``object`` dtypes (:issue:`12541`)
 - Bug in ``.rolling()`` where ``pd.Timedelta`` or ``datetime.timedelta`` was not accepted as a ``window`` argument (:issue:`15440`)
+- Bug in ``Rolling.quantile`` function that caused a segmentation fault when called with a quantile value outside of the range [0, 1] (:issue:`15463`)
 - Bug in ``DataFrame.resample().median()`` if duplicate column names are present (:issue:`14233`)
 
-- Bug in ``DataFrame.groupby().describe()`` when grouping on ``Index`` containing tuples (:issue:`14848`)
-- Bug in creating a ``MultiIndex`` with tuples and not passing a list of names; this will now raise ``ValueError`` (:issue:`15110`)
-- Bug in ``groupby().nunique()`` with a datetimelike-grouper where bins counts were incorrect (:issue:`13453`)
+Sparse
+^^^^^^
 
-- Bug in catching an overflow in ``Timestamp`` + ``Timedelta/Offset`` operations (:issue:`15126`)
-- Bug in the HTML display with with a ``MultiIndex`` and truncation (:issue:`14882`)
+- Bug in ``SparseSeries.reindex`` on single level with list of length 1 (:issue:`15447`)
+- Bug in repr-formatting a ``SparseDataFrame`` after a value was set on (a copy of) one of its series (:issue:`15488`)
+- Bug in ``SparseDataFrame`` construction with lists not coercing to dtype (:issue:`15682`)
 
+Reshaping
+^^^^^^^^^
 
 - Bug in ``pd.merge_asof()`` where ``left_index`` or ``right_index`` caused a failure when multiple ``by`` was specified (:issue:`15676`)
 - Bug in ``pd.merge_asof()`` where ``left_index``/``right_index`` together caused a failure when ``tolerance`` was specified (:issue:`15135`)
 - Bug in ``DataFrame.pivot_table()`` where ``dropna=True`` would not drop all-NaN columns when the columns was a ``category`` dtype (:issue:`15193`)
-
-
-- Bug in ``pd.read_hdf()`` passing a ``Timestamp`` to the ``where`` parameter with a non date column (:issue:`15492`)
-
-
-- Bug in ``Series`` constructor when both ``copy=True`` and ``dtype`` arguments are provided (:issue:`15125`)
-- Bug in ``pd.read_csv()`` for the C engine where ``usecols`` were being indexed incorrectly with ``parse_dates`` (:issue:`14792`)
-- Incorrect dtyped ``Series`` was returned by comparison methods (e.g., ``lt``, ``gt``, ...) against a constant for an empty ``DataFrame`` (:issue:`15077`)
-- Bug in ``Series.dt.round`` inconsistent behaviour on NAT's with different arguments (:issue:`14940`)
-- Bug in ``DataFrame.fillna()`` where the argument ``downcast`` was ignored when fillna value was of type ``dict`` (:issue:`15277`)
-- Bug in ``.reset_index()`` when an all ``NaN`` level of a ``MultiIndex`` would fail (:issue:`6322`)
-
-- Bug in ``pd.read_msgpack()`` when deserializing a ``CategoricalIndex`` (:issue:`15487`)
-- Bug in ``pd.DataFrame.to_records()`` which failed with unicode characters in column names (:issue:`11879`)
-
-
-- Bug in ``pd.read_csv()`` with ``float_precision='round_trip'`` which caused a segfault when a text entry is parsed (:issue:`15140`)
-- Avoid use of ``np.finfo()`` during ``import pandas`` removed to mitigate deadlock on Python GIL misuse (:issue:`14641`)
-
-- Bug in ``DataFrame.to_stata()`` and ``StataWriter`` which produces incorrectly formatted files to be produced for some locales (:issue:`13856`)
-- Bug in ``StataReader`` and ``StataWriter`` which allows invalid encodings (:issue:`15723`)
-- Bug with ``sort=True`` in ``DataFrame.join`` and ``pd.merge`` when joining on indexes (:issue:`15582`)
-
+- Bug in ``pd.melt()`` where passing a tuple value for ``value_vars`` caused a ``TypeError`` (:issue:`15348`)
+- Bug in ``pd.pivot_table()`` where no error was raised when values argument was not in the columns (:issue:`14938`)
 - Bug in ``pd.concat()`` in which concatting with an empty dataframe with ``join='inner'`` was being improperly handled (:issue:`15328`)
-- Bug in ``groupby.agg()`` incorrectly localizing timezone on ``datetime`` (:issue:`15426`, :issue:`10668`, :issue:`13046`)
+- Bug with ``sort=True`` in ``DataFrame.join`` and ``pd.merge`` when joining on indexes (:issue:`15582`)
 
-- Bug in ``SparseDataFrame`` construction with lists not coercing to dtype (:issue:`15682`)
+Numeric
+^^^^^^^
 
-- Bug in ``.read_csv()`` with ``parse_dates`` when multiline headers are specified (:issue:`15376`)
-- Bug in ``groupby.transform()`` that would coerce the resultant dtypes back to the original (:issue:`10972`, :issue:`11444`)
+- Bug in ``.rank()`` which incorrectly ranks ordered categories (:issue:`15420`)
+- Bug in ``.corr()`` and ``.cov()`` where the column and index were the same object (:issue:`14617`)
 - Bug in ``.mode()`` where ``mode`` was not returned if was only a single value (:issue:`15714`)
-
-- Bug in ``DataFrame.hist`` where ``plt.tight_layout`` caused an ``AttributeError``  (use ``matplotlib >= 2.0.1``) (:issue:`9351`)
-- Bug in ``DataFrame.boxplot`` where ``fontsize`` was not applied to the tick labels on both axes (:issue:`15108`)
-- Bug in ``pd.melt()`` where passing a tuple value for ``value_vars`` caused a ``TypeError`` (:issue:`15348`)
+- Bug in ``pd.cut()`` with a single bin on an all 0s array (:issue:`15428`)
+- Bug in ``pd.qcut()`` with a single quantile and an array with identical values (:issue:`15431`)
+- Bug in ``pandas.tools.utils.cartesian_product()`` with large input can cause overflow on windows (:issue:`15265`)
 - Bug in ``.eval()`` which caused multiline evals to fail with local variables not on the first line (:issue:`15342`)
-- Bug in ``pd.read_msgpack()`` which did not allow to load dataframe with an index of type ``CategoricalIndex`` (:issue:`15487`)
+
+Other
+^^^^^
+
+- Compat with SciPy 0.19.0 for testing on ``.interpolate()`` (:issue:`15662`)
+- Compat for 32-bit platforms for ``.qcut/cut``; bins will now be ``int64`` dtype (:issue:`14866`)
+- Require at least 0.23 version of cython to avoid problems with character encodings (:issue:`14699`)
+- Bug in interactions with ``Qt`` when a ``QtApplication`` already exists (:issue:`14372`)
+- Avoid use of ``np.finfo()`` during ``import pandas`` removed to mitigate deadlock on Python GIL misuse (:issue:`14641`)