synch whatsnew/v0.22.0.txt from upstream master

Author: peterpanmj

doc/source/whatsnew/v0.22.0.txt

@@ -17,122 +17,76 @@ New features
 -
 -
 
-.. _whatsnew_0220.enhancements.other:
-
-Other Enhancements
-^^^^^^^^^^^^^^^^^^
-
-correctly calculate ranks for infinit values
-""""""""""""""""""""""""""""""""""""""""""""
-
-In previous versions, ``inf`` elements were assigned ``nan`` as their ranks. Now ranks are calculated properly.
-
-Previous Behavior:
-
-.. code-block:: ipython
-
-    In [17]: pd.Series([-np.inf, 0, 1, np.inf]).rank()
-    Out[17]:
-    0    1.0
-    1    2.0
-    2    3.0
-    3    NaN
-
-Current Behavior
 
-.. code-block:: ipython
+.. _whatsnew_0210.enhancements.get_dummies_dtype:
 
-    In [5]:  pd.Series([-np.inf, 0, 1, np.inf]).rank()
-    Out[5]:
-    0    1.0
-    1    2.0
-    2    3.0
-    3    4.0
-    dtype: float64
+``get_dummies`` now supports ``dtype`` argument
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Furthermore, previously if you rank ``inf`` or ``-inf`` values together with ``nan`` values, results were wrong when using 'top' or 'bottom' argument.
+The :func:`get_dummies` now accepts a ``dtype`` argument, which specifies a dtype for the new columns. The default remains uint8. (:issue:`18330`)
 
-Previously Behavior:
+.. ipython:: python
 
-.. code-block:: ipython
+   df = pd.DataFrame({'a': [1, 2], 'b': [3, 4], 'c': [5, 6]})
+   pd.get_dummies(df, columns=['c']).dtypes
+   pd.get_dummies(df, columns=['c'], dtype=bool).dtypes
 
-    In [15]: pd.Series([np.nan, np.nan, -np.inf, -np.inf]).rank(na_option='top')
-    Out[15]:
-    0    2.5
-    1    2.5
-    2    2.5
-    3    2.5
-    dtype: float64
 
-Current Behavior
-
-.. code-block:: ipython
-
-    In [4]:  pd.Series([np.nan, np.nan, -np.inf, -np.inf]).rank(na_option='top')
-    Out[4]:
-    0    1.5
-    1    1.5
-    2    3.5
-    3    3.5
-    dtype: float64
-
-Moreover, previously if you rank an array of `object` dtype, ``None`` values will have different ranks.
+.. _whatsnew_0220.enhancements.other:
 
-Previously Behavior:
+Other Enhancements
+^^^^^^^^^^^^^^^^^^
 
-.. code-block:: ipython
+- Better support for :func:`Dataframe.style.to_excel` output with the ``xlsxwriter`` engine. (:issue:`16149`)
+- :func:`pandas.tseries.frequencies.to_offset` now accepts leading '+' signs e.g. '+1h'. (:issue:`18171`)
+- :func:`MultiIndex.unique` now supports the ``level=`` argument, to get unique values from a specific index level (:issue:`17896`)
+- :class:`pandas.io.formats.style.Styler` now has method ``hide_index()`` to determine whether the index will be rendered in ouptut (:issue:`14194`)
+- :class:`pandas.io.formats.style.Styler` now has method ``hide_columns()`` to determine whether columns will be hidden in output (:issue:`14194`)
+- Improved wording of ``ValueError`` raised in :func:`to_datetime` when ``unit=`` is passed with a non-convertible value (:issue:`14350`)
+- :func:`Series.fillna` now accepts a Series or a dict as a ``value`` for a categorical dtype (:issue:`17033`)
+- :func:`pandas.read_clipboard` updated to use qtpy, falling back to PyQt5 and then PyQt4, adding compatibility with Python3 and multiple python-qt bindings (:issue:`17722`)
 
-    In [3]:  pd.Series([None, None, None, 'A','B']).rank(na_option='top')
-    Out[3]:
-    0    3.0
-    1    2.0
-    2    1.0
-    3    4.0
-    4    5.0
-    dtype: float64
+.. _whatsnew_0220.api_breaking:
 
-Current Behavior
+Backwards incompatible API changes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. code-block:: ipython
+- :func:`Series.fillna` now raises a ``TypeError`` instead of a ``ValueError`` when passed a list, tuple or DataFrame as a ``value`` (:issue:`18293`)
+- :func:`pandas.DataFrame.merge` no longer casts a ``float`` column to ``object`` when merging on ``int`` and ``float`` columns (:issue:`16572`)
+- The default NA value for :class:`UInt64Index` has changed from 0 to ``NaN``, which impacts methods that mask with NA, such as ``UInt64Index.where()`` (:issue:`18398`)
+-
 
-    In [3]:  pd.Series([None, None, None, 'A','B']).rank(na_option='top')
-    Out[3]:
-    0    2.0
-    1    2.0
-    2    2.0
-    3    4.0
-    4    5.0
 
-- Better support for ``Dataframe.style.to_excel()`` output with the ``xlsxwriter`` engine. (:issue:`16149`)
--
--
 
-.. _whatsnew_0220.api_breaking:
 
-Backwards incompatible API changes
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
--
--
--
 
 .. _whatsnew_0220.api:
 
 Other API Changes
 ^^^^^^^^^^^^^^^^^
 
+- :func:`Series.astype` and :func:`Index.astype` with an incompatible dtype will now raise a ``TypeError`` rather than a ``ValueError`` (:issue:`18231`)
+- ``Series`` construction with an ``object`` dtyped tz-aware datetime and ``dtype=object`` specified, will now return an ``object`` dtyped ``Series``, previously this would infer the datetime dtype (:issue:`18231`)
 - ``NaT`` division with :class:`datetime.timedelta` will now return ``NaN`` instead of raising (:issue:`17876`)
-- All-NaN levels in ``MultiIndex`` are now assigned float rather than object dtype, coherently with flat indexes (:issue:`17929`).
-- :class:`Timestamp` will no longer silently ignore unused or invalid `tz` or `tzinfo` keyword arguments (:issue:`17690`)
-- :class:`Timestamp` will no longer silently ignore invalid `freq` arguments (:issue:`5168`)
-- :class:`CacheableOffset` and :class:`WeekDay` are no longer available in the `tseries.offsets` module (:issue:`17830`)
+- All-NaN levels in a ``MultiIndex`` are now assigned ``float`` rather than ``object`` dtype, promoting consistency with ``Index`` (:issue:`17929`).
+- :class:`Timestamp` will no longer silently ignore unused or invalid ``tz`` or ``tzinfo`` keyword arguments (:issue:`17690`)
+- :class:`Timestamp` will no longer silently ignore invalid ``freq`` arguments (:issue:`5168`)
+- :class:`CacheableOffset` and :class:`WeekDay` are no longer available in the ``pandas.tseries.offsets`` module (:issue:`17830`)
+- `tseries.frequencies.get_freq_group()` and `tseries.frequencies.DAYS` are removed from the public API (:issue:`18034`)
+- :func:`Series.truncate` and :func:`DataFrame.truncate` will raise a ``ValueError`` if the index is not sorted instead of an unhelpful ``KeyError`` (:issue:`17935`)
+- :func:`Index.map` can now accept ``Series`` and dictionary input objects (:issue:`12756`).
+- :func:`Dataframe.unstack` will now default to filling with ``np.nan`` for ``object`` columns. (:issue:`12815`)
+- :class:`IntervalIndex` constructor will raise if the ``closed`` parameter conflicts with how the input data is inferred to be closed (:issue:`18421`)
+- Inserting missing values into indexes will work for all types of indexes and automatically insert the correct type of missing value (``NaN``, ``NaT``, etc.) regardless of the type passed in (:issue:`18295`)
+- Restricted ``DateOffset`` keyword arguments. Previously, ``DateOffset`` subclasses allowed arbitrary keyword arguments which could lead to unexpected behavior. Now, only valid arguments will be accepted. (:issue:`17176`, :issue:`18226`).
 
 .. _whatsnew_0220.deprecations:
 
 Deprecations
 ~~~~~~~~~~~~
 
--
+- ``Series.from_array`` and ``SparseSeries.from_array`` are deprecated. Use the normal constructor ``Series(..)`` and ``SparseSeries(..)`` instead (:issue:`18213`).
 -
 -
 
@@ -141,17 +95,25 @@ Deprecations
 Removal of prior version deprecations/changes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
--
--
--
+- Warnings against the obsolete usage ``Categorical(codes, categories)``, which were emitted for instance when the first two arguments to ``Categorical()`` had different dtypes, and recommended the use of ``Categorical.from_codes``, have now been removed (:issue:`8074`)
+- The ``levels`` and ``labels`` attributes of a ``MultiIndex`` can no longer be set directly (:issue:`4039`).
+- ``pd.tseries.util.pivot_annual`` has been  removed (deprecated since v0.19). Use ``pivot_table`` instead (:issue:`18370`)
+- ``pd.tseries.util.isleapyear`` has been removed (deprecated since v0.19). Use ``.is_leap_year`` property in Datetime-likes instead (:issue:`18370`)
+- ``pd.ordered_merge`` has been removed (deprecated since v0.19). Use ``pd..merge_ordered`` instead (:issue:`18459`)
 
 .. _whatsnew_0220.performance:
 
 Performance Improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
-- Indexers on Series or DataFrame no longer create a reference cycle (:issue:`17956`)
--
+- Indexers on ``Series`` or ``DataFrame`` no longer create a reference cycle (:issue:`17956`)
+- Added a keyword argument, ``cache``, to :func:`to_datetime` that improved the performance of converting duplicate datetime arguments (:issue:`11665`)
+- :class`DateOffset` arithmetic performance is improved (:issue:`18218`)
+- Converting a ``Series`` of ``Timedelta`` objects to days, seconds, etc... sped up through vectorization of underlying methods (:issue:`18092`)
+- Improved performance of ``.map()`` with a ``Series/dict`` input (:issue:`15081`)
+- The overriden ``Timedelta`` properties of days, seconds and microseconds have been removed, leveraging their built-in Python versions instead (:issue:`18242`)
+- ``Series`` construction will reduce the number of copies made of the input data in certain cases (:issue:`17449`)
+- Improved performance of :func:`Series.dt.date` and :func:`DatetimeIndex.date` (:issue:`18058`)
 -
 
 .. _whatsnew_0220.docs:
@@ -168,27 +130,31 @@ Documentation Changes
 Bug Fixes
 ~~~~~~~~~
 
-- Bug in ``pd.read_msgpack()`` with a non existent file is passed in Python 2 (:issue:`15296`)
-- Bug in ``DataFrame.groupby`` where key as tuple in a ``MultiIndex`` were interpreted as a list of keys (:issue:`17979`)
 
 Conversion
 ^^^^^^^^^^
 
--
+- Bug in :class:`Index` constructor with `dtype='uint64'` where int-like floats were not coerced to :class:`UInt64Index` (:issue:`18400`)
 -
 -
 
 Indexing
 ^^^^^^^^
 
-- Bug in :func:`PeriodIndex.truncate` which raises ``TypeError`` when ``PeriodIndex`` is monotonic (:issue:`17717`)
--
+- Bug in :func:`Series.truncate` which raises ``TypeError`` with a monotonic ``PeriodIndex`` (:issue:`17717`)
+- Bug in :func:`DataFrame.groupby` where tuples were interpreted as lists of keys rather than as keys (:issue:`17979`, :issue:`18249`)
+- Bug in :func:`MultiIndex.remove_unused_levels`` which would fill nan values (:issue:`18417`)
+- Bug in :func:`MultiIndex.from_tuples`` which would fail to take zipped tuples in python3 (:issue:`18434`)
+- Bug in :class:`IntervalIndex` where empty and purely NA data was constructed inconsistently depending on the construction method (:issue:`18421`)
 -
 
 I/O
 ^^^
 
 - :func:`read_html` now rewinds seekable IO objects after parse failure, before attempting to parse with a new parser. If a parser errors and the object is non-seekable, an informative error is raised suggesting the use of a different parser (:issue:`17975`)
+- Bug in :func:`read_msgpack` with a non existent file is passed in Python 2 (:issue:`15296`)
+- Bug in :func:`read_csv` where a ``MultiIndex`` with duplicate columns was not being mangled appropriately (:issue:`18062`)
+- Bug in :func:`read_sas` where a file with 0 variables gave an ``AttributeError`` incorrectly. Now it gives an ``EmptyDataError`` (:issue:`18184`)
 -
 -
 
@@ -223,7 +189,7 @@ Reshaping
 Numeric
 ^^^^^^^
 
-- Bug in ``pd.Series.rank()`` and ``pd.DataFrame.rank() could not properly rank infinit values. Infinit values were assigned NaNs as ranks. If NaNs were present together with infinit values, the ranks were calculated wrong (:issue:`6945`)
+-
 -
 -
 
@@ -237,6 +203,6 @@ Categorical
 Other
 ^^^^^
 
--
--
+- Improved error message when attempting to use a Python keyword as an identifier in a numexpr query (:issue:`18221`)
+- Fixed a bug where creating a Series from an array that contains both tz-naive and tz-aware values will result in a Series whose dtype is tz-aware instead of object (:issue:`16406`)
 -