v0.20.0.txt

.. _whatsnew_0200:

v0.20.0 (May 12, 2017)
------------------------

This is a major release from 0.19.2 and includes a small number of API changes, deprecations, new features,
enhancements, and performance improvements along with a large number of bug fixes. We recommend that all
users upgrade to this version.

Highlights include:

- new ``.agg()`` API for Series/DataFrame similar to the groupby-rolling-resample API's, see :ref:`here <whatsnew_0200.enhancements.agg>`
- Integration with the ``feather-format``, including a new top-level ``pd.read_feather()`` and ``DataFrame.to_feather()`` method, see :ref:`here <io.feather>`.
- The ``.ix`` indexer has been deprecated, see :ref:`here <whatsnew_0200.api_breaking.deprecate_ix>`
- ``Panel`` has been deprecated, see :ref:`here <whatsnew_0200.api_breaking.deprecate_panel>`
- Addition of an ``IntervalIndex`` and ``Interval`` scalar type, see :ref:`here <whatsnew_0200.enhancements.intervalindex>`
- Improved user API when accessing levels in ``.groupby()``, see :ref:`here <whatsnew_0200.enhancements.groupby_access>`
- Improved support for ``UInt64`` dtypes, see :ref:`here <whatsnew_0200.enhancements.uint64_support>`
- A new orient for JSON serialization, ``orient='table'``, that uses the :ref:`Table Schema spec <whatsnew_0200.enhancements.table_schema>`
- Experimental support for exporting ``DataFrame.style`` formats to Excel , see :ref:`here <whatsnew_0200.enhancements.style_excel>`
- Window Binary Corr/Cov operations now return a MultiIndexed ``DataFrame`` rather than a ``Panel``, as ``Panel`` is now deprecated, see :ref:`here <whatsnew_0200.api_breaking.rolling_pairwise>`
- Support for S3 handling now uses ``s3fs``, see :ref:`here <whatsnew_0200.api_breaking.s3>`
- Google BigQuery support now uses the ``pandas-gbq`` library, see :ref:`here <whatsnew_0200.api_breaking.gbq>`
- Switched the test framework to use `pytest <http://doc.pytest.org/en/latest>`__ (:issue:`13097`)

.. warning::

  Pandas has changed the internal structure and layout of the codebase.
  This can affect imports that are not from the top-level ``pandas.*`` namespace, please see the changes :ref:`here <whatsnew_0200.privacy>`.

Check the :ref:`API Changes <whatsnew_0200.api_breaking>` and :ref:`deprecations <whatsnew_0200.deprecations>` before updating.

.. contents:: What's new in v0.20.0
    :local:
    :backlinks: none

.. _whatsnew_0200.enhancements:

New features
~~~~~~~~~~~~

.. _whatsnew_0200.enhancements.agg:

``agg`` API
^^^^^^^^^^^

Series & DataFrame have been enhanced to support the aggregation API. This is an already familiar API that
is supported for groupby, window operations, and resampling. This allows one to express, possibly multiple
aggregation operations, in a single concise way by using :meth:`~DataFrame.agg`,
and :meth:`~DataFrame.transform`. The full documentation is :ref:`here <basics.aggregate>` (:issue:`1623`)

Here is a sample

.. ipython:: python

   df = pd.DataFrame(np.random.randn(10, 3), columns=['A', 'B', 'C'],
                    index=pd.date_range('1/1/2000', periods=10))
   df.iloc[3:7] = np.nan
   df

One can operate using string function names, callables, lists, or dictionaries of these.

Using a single function is equivalent to ``.apply``.

.. ipython:: python

   df.agg('sum')

Multiple functions in lists.

.. ipython:: python

   df.agg(['sum', 'min'])

Using a dict provides the ability to have selective aggregation per column.
You will get a matrix-like output of all of the aggregators. The output will consist
of all unique functions. Those that are not noted for a particular column will be ``NaN``:

.. ipython:: python

   df.agg({'A' : ['sum', 'min'], 'B' : ['min', 'max']})

The API also supports a ``.transform()`` function to provide for broadcasting results.

.. ipython:: python

   df.transform(['abs', lambda x: x - x.min()])

When presented with mixed dtypes that cannot aggregate, ``.agg()`` will only take the valid
aggregations. This is similiar to how groupby ``.agg()`` works. (:issue:`15015`)

.. ipython:: python

   df = pd.DataFrame({'A': [1, 2, 3],
                      'B': [1., 2., 3.],
                      'C': ['foo', 'bar', 'baz'],
                      'D': pd.date_range('20130101', periods=3)})
   df.dtypes

.. ipython:: python

   df.agg(['min', 'sum'])

.. _whatsnew_0200.enhancements.dataio_dtype:

``dtype`` keyword for data IO
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The ``dtype`` keyword argument in the :func:`read_csv` function for specifying the types of parsed columns is now supported with the ``'python'`` engine (:issue:`14295`). See the :ref:`io docs <io.dtypes>` for more information.

.. ipython:: python
   :suppress:

   from pandas.compat import StringIO

.. ipython:: python

   data = "a,b\n1,2\n3,4"
   pd.read_csv(StringIO(data), engine='python').dtypes
   pd.read_csv(StringIO(data), engine='python', dtype={'a':'float64', 'b':'object'}).dtypes

The ``dtype`` keyword argument is also now supported in the :func:`read_fwf` function for parsing
fixed-width text files, and :func:`read_excel` for parsing Excel files.

.. ipython:: python

   data = "a  b\n1  2\n3  4"
   pd.read_fwf(StringIO(data)).dtypes
   pd.read_fwf(StringIO(data), dtype={'a':'float64', 'b':'object'}).dtypes

.. _whatsnew_0120.enhancements.datetime_origin:

``.to_datetime()`` has gained an ``origin`` parameter
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

:func:`to_datetime` has gained a new parameter, ``origin``, to define a reference date
from where to compute the resulting ``DatetimeIndex`` when ``unit`` is specified. (:issue:`11276`, :issue:`11745`)

Start with 1960-01-01 as the starting date

.. ipython:: python

   pd.to_datetime([1, 2, 3], unit='D', origin=pd.Timestamp('1960-01-01'))

The default is set at ``origin='unix'``, which defaults to ``1970-01-01 00:00:00``.
Commonly called 'unix epoch' or POSIX time. This was the previous default, so this is a backward compatible change.

.. ipython:: python

   pd.to_datetime([1, 2, 3], unit='D')

.. _whatsnew_0200.enhancements.errors:

``pandas.errors``
^^^^^^^^^^^^^^^^^

We are adding a standard public module for all pandas exceptions & warnings ``pandas.errors``. (:issue:`14800`). Previously
these exceptions & warnings could be imported from ``pandas.core.common`` or ``pandas.io.common``. These exceptions and warnings
will be removed from the ``*.common`` locations in a future release. (:issue:`15541`)

The following are now part of this API:

.. code-block:: python

   ['DtypeWarning',
    'EmptyDataError',
    'OutOfBoundsDatetime',
    'ParserError',
    'ParserWarning',
    'PerformanceWarning',
    'UnsortedIndexError',
    'UnsupportedFunctionCall']


.. _whatsnew_0200.enhancements.testing:

``pandas.testing``
^^^^^^^^^^^^^^^^^^

We are adding a standard module that exposes the public testing functions in ``pandas.testing`` (:issue:`9895`). Those functions can be used when writing tests for functionality using pandas objects.

The following testing functions are now part of this API:

- :func:`testing.assert_frame_equal`
- :func:`testing.assert_series_equal`
- :func:`testing.assert_index_equal`


.. _whatsnew_0200.enhancements.groupby_access:

Groupby Enhancements
^^^^^^^^^^^^^^^^^^^^

Strings passed to ``DataFrame.groupby()`` as the ``by`` parameter may now reference either column names or index level names (:issue:`5677`)

.. ipython:: python

   arrays = [['bar', 'bar', 'baz', 'baz', 'foo', 'foo', 'qux', 'qux'],
             ['one', 'two', 'one', 'two', 'one', 'two', 'one', 'two']]

   index = pd.MultiIndex.from_arrays(arrays, names=['first', 'second'])

   df = pd.DataFrame({'A': [1, 1, 1, 1, 2, 2, 3, 3],
                      'B': np.arange(8)},
                     index=index)
   df

   df.groupby(['second', 'A']).sum()

.. _whatsnew_0200.enhancements.compressed_urls:

Better support for compressed URLs in ``read_csv``
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The compression code was refactored (:issue:`12688`). As a result, reading
dataframes from URLs in :func:`read_csv` or :func:`read_table` now supports
additional compression methods: ``xz``, ``bz2``, and ``zip`` (:issue:`14570`).
Previously, only ``gzip`` compression was supported. By default, compression of
URLs and paths are now both inferred using their file extensions. Additionally,
support for bz2 compression in the python 2 c-engine improved (:issue:`14874`).

.. ipython:: python

   url = 'https://github.com/{repo}/raw/{branch}/{path}'.format(
       repo = 'pandas-dev/pandas',
       branch = 'master',
       path = 'pandas/tests/io/parser/data/salaries.csv.bz2',
   )
   df = pd.read_table(url, compression='infer')  # default, infer compression
   df = pd.read_table(url, compression='bz2')  # explicitly specify compression
   df.head(2)

.. _whatsnew_0200.enhancements.pickle_compression:

Pickle file I/O now supports compression
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

:func:`read_pickle`, :meth:`DataFame.to_pickle` and :meth:`Series.to_pickle`
can now read from and write to compressed pickle files. Compression methods
can be an explicit parameter or be inferred from the file extension.
See :ref:`the docs here <io.pickle.compression>`

.. ipython:: python

   df = pd.DataFrame({
       'A': np.random.randn(1000),
       'B': 'foo',
       'C': pd.date_range('20130101', periods=1000, freq='s')})

Using an explicit compression type

.. ipython:: python

   df.to_pickle("data.pkl.compress", compression="gzip")
   rt = pd.read_pickle("data.pkl.compress", compression="gzip")
   rt

Inferring compression type from the extension

.. ipython:: python

   df.to_pickle("data.pkl.xz", compression="infer")
   rt = pd.read_pickle("data.pkl.xz", compression="infer")
   rt

The default is to ``infer``:

.. ipython:: python

   df.to_pickle("data.pkl.gz")
   rt = pd.read_pickle("data.pkl.gz")
   rt
   df["A"].to_pickle("s1.pkl.bz2")
   rt = pd.read_pickle("s1.pkl.bz2")
   rt

.. ipython:: python
   :suppress:

   import os
   os.remove("data.pkl.compress")
   os.remove("data.pkl.xz")
   os.remove("data.pkl.gz")
   os.remove("s1.pkl.bz2")

.. _whatsnew_0200.enhancements.uint64_support:

UInt64 Support Improved
^^^^^^^^^^^^^^^^^^^^^^^

Pandas has significantly improved support for operations involving unsigned,
or purely non-negative, integers. Previously, handling these integers would
result in improper rounding or data-type casting, leading to incorrect results.
Notably, a new numerical index, ``UInt64Index``, has been created (:issue:`14937`)

.. ipython:: python

   idx = pd.UInt64Index([1, 2, 3])
   df = pd.DataFrame({'A': ['a', 'b', 'c']}, index=idx)
   df.index

- Bug in converting object elements of array-like objects to unsigned 64-bit integers (:issue:`4471`, :issue:`14982`)
- Bug in ``Series.unique()`` in which unsigned 64-bit integers were causing overflow (:issue:`14721`)
- Bug in ``DataFrame`` construction in which unsigned 64-bit integer elements were being converted to objects (:issue:`14881`)
- Bug in ``pd.read_csv()`` in which unsigned 64-bit integer elements were being improperly converted to the wrong data types (:issue:`14983`)
- Bug in ``pd.unique()`` in which unsigned 64-bit integers were causing overflow (:issue:`14915`)
- Bug in ``pd.value_counts()`` in which unsigned 64-bit integers were being erroneously truncated in the output (:issue:`14934`)

.. _whatsnew_0200.enhancements.groupy_categorical:

GroupBy on Categoricals
^^^^^^^^^^^^^^^^^^^^^^^

In previous versions, ``.groupby(..., sort=False)`` would fail with a ``ValueError`` when grouping on a categorical series with some categories not appearing in the data. (:issue:`13179`)

.. ipython:: python

  chromosomes = np.r_[np.arange(1, 23).astype(str), ['X', 'Y']]
  df = pd.DataFrame({
      'A': np.random.randint(100),
      'B': np.random.randint(100),
      'C': np.random.randint(100),
      'chromosomes': pd.Categorical(np.random.choice(chromosomes, 100),
                                    categories=chromosomes,
                                    ordered=True)})
  df

Previous Behavior:

.. code-block:: ipython

  In [3]: df[df.chromosomes != '1'].groupby('chromosomes', sort=False).sum()
  ---------------------------------------------------------------------------
  ValueError: items in new_categories are not the same as in old categories

New Behavior:

.. ipython:: python

  df[df.chromosomes != '1'].groupby('chromosomes', sort=False).sum()

.. _whatsnew_0200.enhancements.table_schema:

Table Schema Output
^^^^^^^^^^^^^^^^^^^

The new orient ``'table'`` for :meth:`DataFrame.to_json`
will generate a `Table Schema`_ compatible string representation of
the data.

.. ipython:: python

   df = pd.DataFrame(
       {'A': [1, 2, 3],
        'B': ['a', 'b', 'c'],
        'C': pd.date_range('2016-01-01', freq='d', periods=3),
       }, index=pd.Index(range(3), name='idx'))
   df
   df.to_json(orient='table')


See :ref:`IO: Table Schema for more<io.table_schema>`.

Additionally, the repr for ``DataFrame`` and ``Series`` can now publish
this JSON Table schema representation of the Series or DataFrame if you are
using IPython (or another frontend like `nteract`_ using the Jupyter messaging
protocol).
This gives frontends like the Jupyter notebook and `nteract`_
more flexiblity in how they display pandas objects, since they have
more information about the data.
You must enable this by setting the ``display.html.table_schema`` option to ``True``.

.. _Table Schema: http://specs.frictionlessdata.io/json-table-schema/
.. _nteract: http://nteract.io/

.. _whatsnew_0200.enhancements.scipy_sparse:

SciPy sparse matrix from/to SparseDataFrame
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Pandas now supports creating sparse dataframes directly from ``scipy.sparse.spmatrix`` instances.
See the :ref:`documentation <sparse.scipysparse>` for more information. (:issue:`4343`)

All sparse formats are supported, but matrices that are not in :mod:`COOrdinate <scipy.sparse>` format will be converted, copying data as needed.

.. ipython:: python

   from scipy.sparse import csr_matrix
   arr = np.random.random(size=(1000, 5))
   arr[arr < .9] = 0
   sp_arr = csr_matrix(arr)
   sp_arr
   sdf = pd.SparseDataFrame(sp_arr)
   sdf

To convert a ``SparseDataFrame`` back to sparse SciPy matrix in COO format, you can use:

.. ipython:: python

   sdf.to_coo()

.. _whatsnew_0200.enhancements.style_excel:

Excel output for styled DataFrames
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Experimental support has been added to export ``DataFrame.style`` formats to Excel using the ``openpyxl`` engine. (:issue:`15530`)

For example, after running the following, ``styled.xlsx`` renders as below:

.. ipython:: python

    np.random.seed(24)
    df = pd.DataFrame({'A': np.linspace(1, 10, 10)})
    df = pd.concat([df, pd.DataFrame(np.random.RandomState(24).randn(10, 4),
                                     columns=list('BCDE'))],
                   axis=1)
    df.iloc[0, 2] = np.nan
    df
    styled = df.style.\
        applymap(lambda val: 'color: %s' % 'red' if val < 0 else 'black').\
        apply(lambda s: ['background-color: yellow' if v else ''
                         for v in s == s.max()])
    styled.to_excel('styled.xlsx', engine='openpyxl')

.. image:: _static/style-excel.png

.. ipython:: python
    :suppress:
    import os
    os.remove('styled.xlsx')

See the :ref:`Style documentation <style.ipynb>` for more detail.

.. _whatsnew_0200.enhancements.intervalindex:

IntervalIndex
^^^^^^^^^^^^^

pandas has gained an ``IntervalIndex`` with its own dtype, ``interval`` as well as the ``Interval`` scalar type. These allow first-class support for interval
notation, specifically as a return type for the categories in :func:`cut` and :func:`qcut`. The ``IntervalIndex`` allows some unique indexing, see the
:ref:`docs <indexing.intervallindex>`. (:issue:`7640`, :issue:`8625`)

Previous behavior:

The returned categories were strings, representing Intervals

.. code-block:: ipython

   In [1]: c = pd.cut(range(4), bins=2)

   In [2]: c
   Out[2]:
   [(-0.003, 1.5], (-0.003, 1.5], (1.5, 3], (1.5, 3]]
   Categories (2, object): [(-0.003, 1.5] < (1.5, 3]]

   In [3]: c.categories
   Out[3]: Index(['(-0.003, 1.5]', '(1.5, 3]'], dtype='object')

New behavior:

.. ipython:: python

   c = pd.cut(range(4), bins=2)
   c
   c.categories

Furthermore, this allows one to bin *other* data with these same bins, with ``NaN`` represents a missing
value similar to other dtypes.

.. ipython:: python

   pd.cut([0, 3, 5, 1], bins=c.categories)

An ``IntervalIndex`` can also be used in ``Series`` and ``DataFrame`` as the index.

.. ipython:: python

   df = pd.DataFrame({'A': range(4),
                      'B': pd.cut([0, 3, 1, 1], bins=c.categories)}
                    ).set_index('B')
   df

Selecting via a specific interval:

.. ipython:: python

   df.loc[pd.Interval(1.5, 3.0)]

Selecting via a scalar value that is contained *in* the intervals.

.. ipython:: python

   df.loc[0]

.. _whatsnew_0200.enhancements.other:

Other Enhancements
^^^^^^^^^^^^^^^^^^

- ``DataFrame.rolling()`` now accepts the parameter ``closed='right'|'left'|'both'|'neither'`` to choose the rolling window endpoint closedness. See the :ref:`documentation <stats.rolling_window.endpoints>` (:issue:`13965`)
- Integration with the ``feather-format``, including a new top-level ``pd.read_feather()`` and ``DataFrame.to_feather()`` method, see :ref:`here <io.feather>`.
- ``Series.str.replace()`` now accepts a callable, as replacement, which is passed to ``re.sub`` (:issue:`15055`)
- ``Series.str.replace()`` now accepts a compiled regular expression as a pattern (:issue:`15446`)
- ``Series.sort_index`` accepts parameters ``kind`` and ``na_position`` (:issue:`13589`, :issue:`14444`)
- ``DataFrame`` has gained a ``nunique()`` method to count the distinct values over an axis (:issue:`14336`).
- ``DataFrame`` has gained a ``melt()`` method, equivalent to ``pd.melt()``, for unpivoting from a wide to long format (:issue:`12640`).
- ``DataFrame.groupby()`` has gained a ``.nunique()`` method to count the distinct values for all columns within each group (:issue:`14336`, :issue:`15197`).

- ``pd.read_excel()`` now preserves sheet order when using ``sheetname=None`` (:issue:`9930`)
- Multiple offset aliases with decimal points are now supported (e.g. ``0.5min`` is parsed as ``30s``) (:issue:`8419`)
- ``.isnull()`` and ``.notnull()`` have been added to ``Index`` object to make them more consistent with the ``Series`` API (:issue:`15300`)

- New ``UnsortedIndexError`` (subclass of ``KeyError``) raised when indexing/slicing into an
  unsorted MultiIndex (:issue:`11897`). This allows differentiation between errors due to lack
  of sorting or an incorrect key. See :ref:`here <advanced.unsorted>`
- ``MultiIndex`` has gained a ``.to_frame()`` method to convert to a ``DataFrame`` (:issue:`12397`)
- ``pd.cut`` and ``pd.qcut`` now support datetime64 and timedelta64 dtypes (:issue:`14714`, :issue:`14798`)
- ``pd.qcut`` has gained the ``duplicates='raise'|'drop'`` option to control whether to raise on duplicated edges (:issue:`7751`)
- ``Series`` provides a ``to_excel`` method to output Excel files (:issue:`8825`)
- The ``usecols`` argument in ``pd.read_csv()`` now accepts a callable function as a value  (:issue:`14154`)
- The ``skiprows`` argument in ``pd.read_csv()`` now accepts a callable function as a value  (:issue:`10882`)
- The ``nrows`` and ``chunksize`` arguments in ``pd.read_csv()`` are supported if both are passed (:issue:`6774`, :issue:`15755`)
- ``DataFrame.plot`` now prints a title above each subplot if ``suplots=True`` and ``title`` is a list of strings (:issue:`14753`)
- ``DataFrame.plot`` can pass the matplotlib 2.0 default color cycle as a single string as color parameter, see `here <http://matplotlib.org/2.0.0/users/colors.html#cn-color-selection>`__. (:issue:`15516`)
- ``Series.interpolate()`` now supports timedelta as an index type with ``method='time'`` (:issue:`6424`)
- Addition of a ``level`` keyword to ``DataFrame/Series.rename`` to rename
  labels in the specified level of a MultiIndex (:issue:`4160`).
- ``Timedelta.isoformat`` method added for formatting Timedeltas as an `ISO 8601 duration`_. See the :ref:`Timedelta docs <timedeltas.isoformat>` (:issue:`15136`)
- ``.select_dtypes()`` now allows the string ``datetimetz`` to generically select datetimes with tz (:issue:`14910`)
- The ``.to_latex()`` method will now accept ``multicolumn`` and ``multirow`` arguments to use the accompanying LaTeX enhancements

- ``pd.merge_asof()`` gained the option ``direction='backward'|'forward'|'nearest'`` (:issue:`14887`)
- ``Series/DataFrame.asfreq()`` have gained a ``fill_value`` parameter, to fill missing values (:issue:`3715`).
- ``Series/DataFrame.resample.asfreq`` have gained a ``fill_value`` parameter, to fill missing values during resampling (:issue:`3715`).
- ``pandas.tools.hashing`` has gained a ``hash_tuples`` routine, and ``hash_pandas_object`` has gained the ability to hash a ``MultiIndex`` (:issue:`15224`)
- ``Series/DataFrame.squeeze()`` have gained the ``axis`` parameter. (:issue:`15339`)
- ``DataFrame.to_excel()`` has a new ``freeze_panes`` parameter to turn on Freeze Panes when exporting to Excel (:issue:`15160`)
- ``pd.read_html()`` will parse multiple header rows, creating a multiindex header. (:issue:`13434`).
- HTML table output skips ``colspan`` or ``rowspan`` attribute if equal to 1. (:issue:`15403`)
- ``pd.io.api.Styler`` template now has blocks for easier extension, :ref:`see the example notebook <style.ipynb#Subclassing>` (:issue:`15649`)
- ``pd.io.api.Styler.render`` now accepts ``**kwargs`` to allow user-defined variables in the template (:issue:`15649`)


- ``TimedeltaIndex`` now has a custom datetick formatter specifically designed for nanosecond level precision (:issue:`8711`)
- ``pd.api.types.union_categoricals`` gained the ``ignore_ordered`` argument to allow ignoring the ordered attribute of unioned categoricals (:issue:`13410`). See the :ref:`categorical union docs <categorical.union>` for more information.
- ``DataFrame.to_latex()`` and ``DataFrame.to_string()`` now allow optional header aliases. (:issue:`15536`)
- Re-enable the ``parse_dates`` keyword of ``pd.read_excel()`` to parse string columns as dates (:issue:`14326`)
- Added ``.empty`` property to subclasses of ``Index``. (:issue:`15270`)
- Enabled floor division for ``Timedelta`` and ``TimedeltaIndex`` (:issue:`15828`)
- ``pandas.io.json.json_normalize()`` gained the option ``errors='ignore'|'raise'``; the default is ``errors='raise'`` which is backward compatible. (:issue:`14583`)
- ``pandas.io.json.json_normalize()`` with an empty ``list`` will return an empty ``DataFrame`` (:issue:`15534`)
- ``pandas.io.json.json_normalize()`` has gained a ``sep`` option that accepts ``str`` to separate joined fields; the default is ".", which is backward compatible. (:issue:`14883`)
- :meth:`~MultiIndex.remove_unused_levels` has been added to facilitate :ref:`removing unused levels <advanced.shown_levels>`. (:issue:`15694`)
- ``pd.read_csv()`` will now raise a ``ParserError`` error whenever any parsing error occurs (:issue:`15913`, :issue:`15925`)
- ``pd.read_csv()`` now supports the ``error_bad_lines`` and ``warn_bad_lines`` arguments for the Python parser (:issue:`15925`)
- The ``display.show_dimensions`` option can now also be used to specify
  whether the length of a ``Series`` should be shown in its repr (:issue:`7117`).
- ``parallel_coordinates()`` has gained a ``sort_labels`` keyword arg that sorts class labels and the colours assigned to them (:issue:`15908`)


.. _ISO 8601 duration: https://en.wikipedia.org/wiki/ISO_8601#Durations


.. _whatsnew_0200.api_breaking:

Backwards incompatible API changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. _whatsnew_0200.api_breaking.deprecate_ix:

Deprecate .ix
^^^^^^^^^^^^^

The ``.ix`` indexer is deprecated, in favor of the more strict ``.iloc`` and ``.loc`` indexers. ``.ix`` offers a lot of magic on the inference of what the user wants to do. To wit, ``.ix`` can decide to index *positionally* OR via *labels*, depending on the data type of the index. This has caused quite a bit of user confusion over the years. The full indexing documentation are :ref:`here <indexing>`. (:issue:`14218`)


The recommended methods of indexing are:

- ``.loc`` if you want to *label* index
- ``.iloc`` if you want to *positionally* index.

Using ``.ix`` will now show a ``DeprecationWarning`` with a link to some examples of how to convert code :ref:`here <indexing.deprecate_ix>`.


.. ipython:: python

  df = pd.DataFrame({'A': [1, 2, 3],
                     'B': [4, 5, 6]},
                    index=list('abc'))

  df

Previous Behavior, where you wish to get the 0th and the 2nd elements from the index in the 'A' column.

.. code-block:: ipython

  In [3]: df.ix[[0, 2], 'A']
  Out[3]:
  a    1
  c    3
  Name: A, dtype: int64

Using ``.loc``. Here we will select the appropriate indexes from the index, then use *label* indexing.

.. ipython:: python

  df.loc[df.index[[0, 2]], 'A']

Using ``.iloc``. Here we will get the location of the 'A' column, then use *positional* indexing to select things.

.. ipython:: python

  df.iloc[[0, 2], df.columns.get_loc('A')]


.. _whatsnew_0200.api_breaking.deprecate_panel:

Deprecate Panel
^^^^^^^^^^^^^^^

``Panel`` is deprecated and will be removed in a future version. The recommended way to represent 3-D data are
with a ``MultiIndex`` on a ``DataFrame`` via the :meth:`~Panel.to_frame` or with the `xarray package <http://xarray.pydata.org/en/stable/>`__. Pandas
provides a :meth:`~Panel.to_xarray` method to automate this conversion. See the documentation :ref:`Deprecate Panel <dsintro.deprecate_panel>`. (:issue:`13563`).

.. ipython:: python
   :okwarning:

   p = tm.makePanel()
   p

Convert to a MultiIndex DataFrame

.. ipython:: python

   p.to_frame()

Convert to an xarray DataArray

.. ipython:: python

   p.to_xarray()

.. _whatsnew_0200.api_breaking.deprecate_group_agg_dict:

Deprecate groupby.agg() with a dictionary when renaming
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The ``.groupby(..).agg(..)``, ``.rolling(..).agg(..)``, and ``.resample(..).agg(..)``  syntax can accept a variable of inputs, including scalars,
list, and a dict of column names to scalars or lists. This provides a useful syntax for constructing multiple
(potentially different) aggregations.

However, ``.agg(..)`` can *also* accept a dict that allows 'renaming' of the result columns. This is a complicated and confusing syntax, as well as not consistent
between ``Series`` and ``DataFrame``. We are deprecating this 'renaming' functionaility.

- We are deprecating passing a dict to a grouped/rolled/resampled ``Series``. This allowed
  one to ``rename`` the resulting aggregation, but this had a completely different
  meaning than passing a dictionary to a grouped ``DataFrame``, which accepts column-to-aggregations.
- We are deprecating passing a dict-of-dicts to a grouped/rolled/resampled ``DataFrame`` in a similar manner.

This is an illustrative example:

.. ipython:: python

    df = pd.DataFrame({'A': [1, 1, 1, 2, 2],
                       'B': range(5),
                       'C': range(5)})
    df

Here is a typical useful syntax for computing different aggregations for different columns. This
is a natural, and useful syntax. We aggregate from the dict-to-list by taking the specified
columns and applying the list of functions. This returns a ``MultiIndex`` for the columns.

.. ipython:: python

   df.groupby('A').agg({'B': 'sum', 'C': 'min'})

Here's an example of the first deprecation, passing a dict to a grouped ``Series``. This
is a combination aggregation & renaming:

.. code-block:: ipython

   In [6]: df.groupby('A').B.agg({'foo': 'count'})
   FutureWarning: using a dict on a Series for aggregation
   is deprecated and will be removed in a future version

   Out[6]:
      foo
   A
   1    3
   2    2

You can accomplish the same operation, more idiomatically by:

.. ipython:: python

   df.groupby('A').B.agg(['count']).rename(columns={'count': 'foo'})


Here's an example of the second deprecation, passing a dict-of-dict to a grouped ``DataFrame``:

.. code-block:: python

   In [23]: (df.groupby('A')
               .agg({'B': {'foo': 'sum'}, 'C': {'bar': 'min'}})
            )
   FutureWarning: using a dict with renaming is deprecated and
   will be removed in a future version

   Out[23]:
        B   C
      foo bar
   A
   1   3   0
   2   7   3


You can accomplish nearly the same by:

.. ipython:: python

   (df.groupby('A')
      .agg({'B': 'sum', 'C': 'min'})
      .rename(columns={'B': 'foo', 'C': 'bar'})
   )

.. _whatsnew.api_breaking.io_compat:

Possible incompat for HDF5 formats for pandas < 0.13.0
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

``pd.TimeSeries`` was deprecated officially in 0.17.0, though has only been an alias since 0.13.0. It has
been dropped in favor of ``pd.Series``. (:issue:`15098`).

This *may* cause HDF5 files that were created in prior versions to become unreadable if ``pd.TimeSeries``
was used. This is most likely to be for pandas < 0.13.0. If you find yourself in this situation.
You can use a recent prior version of pandas to read in your HDF5 files,
then write them out again after applying the procedure below.

.. code-block:: ipython

   In [2]: s = pd.TimeSeries([1,2,3], index=pd.date_range('20130101', periods=3))

   In [3]: s
   Out[3]:
   2013-01-01    1
   2013-01-02    2
   2013-01-03    3
   Freq: D, dtype: int64

   In [4]: type(s)
   Out[4]: pandas.core.series.TimeSeries

   In [5]: s = pd.Series(s)

   In [6]: s
   Out[6]:
   2013-01-01    1
   2013-01-02    2
   2013-01-03    3
   Freq: D, dtype: int64

   In [7]: type(s)
   Out[7]: pandas.core.series.Series


.. _whatsnew_0200.api_breaking.index_map:

Map on Index types now return other Index types
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

``map`` on an ``Index`` now returns an ``Index``, not a numpy array (:issue:`12766`)

.. ipython:: python

   idx = Index([1, 2])
   idx
   mi = MultiIndex.from_tuples([(1, 2), (2, 4)])
   mi

Previous Behavior:

.. code-block:: ipython

   In [5]: idx.map(lambda x: x * 2)
   Out[5]: array([2, 4])

   In [6]: idx.map(lambda x: (x, x * 2))
   Out[6]: array([(1, 2), (2, 4)], dtype=object)

   In [7]: mi.map(lambda x: x)
   Out[7]: array([(1, 2), (2, 4)], dtype=object)

   In [8]: mi.map(lambda x: x[0])
   Out[8]: array([1, 2])

New Behavior:

.. ipython:: python

   idx.map(lambda x: x * 2)
   idx.map(lambda x: (x, x * 2))

   mi.map(lambda x: x)

   mi.map(lambda x: x[0])


``map`` on a ``Series`` with ``datetime64`` values may return ``int64`` dtypes rather than ``int32``

.. ipython:: python

   s = Series(date_range('2011-01-02T00:00', '2011-01-02T02:00', freq='H').tz_localize('Asia/Tokyo'))
   s

Previous Behavior:

.. code-block:: ipython

   In [9]: s.map(lambda x: x.hour)
   Out[9]:
   0    0
   1    1
   2    2
   dtype: int32

New Behavior:

.. ipython:: python

   s.map(lambda x: x.hour)


.. _whatsnew_0200.api_breaking.index_dt_field:

Accessing datetime fields of Index now return Index
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The datetime-related attributes (see :ref:`here <timeseries.components>`
for an overview) of ``DatetimeIndex``, ``PeriodIndex`` and ``TimedeltaIndex`` previously
returned numpy arrays. They will now return a new ``Index`` object, except
in the case of a boolean field, where the result will stil be a boolean ndarray. (:issue:`15022`)

Previous behaviour:

.. code-block:: ipython

    In [1]: idx = pd.date_range("2015-01-01", periods=5, freq='10H')

    In [2]: idx.hour
    Out[2]: array([ 0, 10, 20,  6, 16], dtype=int32)

New Behavior:

.. ipython:: python

    idx = pd.date_range("2015-01-01", periods=5, freq='10H')
    idx.hour

This has the advantage that specific ``Index`` methods are still available on the
result. On the other hand, this might have backward incompatibilities: e.g.
compared to numpy arrays, ``Index`` objects are not mutable. To get the original
ndarray, you can always convert explicitly using ``np.asarray(idx.hour)``.

.. _whatsnew_0200.api_breaking.unique:

pd.unique will now be consistent with extension types
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In prior versions, using ``Series.unique()`` and :func:`unique` on ``Categorical`` and tz-aware
datatypes would yield different return types. These are now made consistent. (:issue:`15903`)

- Datetime tz-aware

  Previous behaviour:

  .. code-block:: ipython

     # Series
     In [5]: pd.Series([pd.Timestamp('20160101', tz='US/Eastern'),
                        pd.Timestamp('20160101', tz='US/Eastern')]).unique()
     Out[5]: array([Timestamp('2016-01-01 00:00:00-0500', tz='US/Eastern')], dtype=object)

     In [6]: pd.unique(pd.Series([pd.Timestamp('20160101', tz='US/Eastern'),
                                  pd.Timestamp('20160101', tz='US/Eastern')]))
     Out[6]: array(['2016-01-01T05:00:00.000000000'], dtype='datetime64[ns]')

     # Index
     In [7]: pd.Index([pd.Timestamp('20160101', tz='US/Eastern'),
                       pd.Timestamp('20160101', tz='US/Eastern')]).unique()
     Out[7]: DatetimeIndex(['2016-01-01 00:00:00-05:00'], dtype='datetime64[ns, US/Eastern]', freq=None)

     In [8]: pd.unique([pd.Timestamp('20160101', tz='US/Eastern'),
                        pd.Timestamp('20160101', tz='US/Eastern')])
     Out[8]: array(['2016-01-01T05:00:00.000000000'], dtype='datetime64[ns]')

  New Behavior:

  .. ipython:: python

     # Series, returns an array of Timestamp tz-aware
     pd.Series([pd.Timestamp('20160101', tz='US/Eastern'),
               pd.Timestamp('20160101', tz='US/Eastern')]).unique()
     pd.unique(pd.Series([pd.Timestamp('20160101', tz='US/Eastern'),
                          pd.Timestamp('20160101', tz='US/Eastern')]))

     # Index, returns a DatetimeIndex
     pd.Index([pd.Timestamp('20160101', tz='US/Eastern'),
               pd.Timestamp('20160101', tz='US/Eastern')]).unique()
     pd.unique(pd.Index([pd.Timestamp('20160101', tz='US/Eastern'),
                         pd.Timestamp('20160101', tz='US/Eastern')]))

- Categoricals

  Previous behaviour:

  .. code-block:: ipython

     In [1]: pd.Series(pd.Categorical(list('baabc'))).unique()
     Out[1]:
     [b, a, c]
     Categories (3, object): [b, a, c]

     In [2]: pd.unique(pd.Series(pd.Categorical(list('baabc'))))
     Out[2]: array(['b', 'a', 'c'], dtype=object)

  New Behavior:

  .. ipython:: python

     # returns a Categorical
     pd.Series(pd.Categorical(list('baabc'))).unique()
     pd.unique(pd.Series(pd.Categorical(list('baabc'))).unique())

.. _whatsnew_0200.api_breaking.s3:

S3 File Handling
^^^^^^^^^^^^^^^^

pandas now uses `s3fs <http://s3fs.readthedocs.io/>`_ for handling S3 connections. This shouldn't break
any code. However, since ``s3fs`` is not a required dependency, you will need to install it separately, like ``boto``
in prior versions of pandas. (:issue:`11915`).

.. _whatsnew_0200.api_breaking.partial_string_indexing:

Partial String Indexing Changes
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

:ref:`DatetimeIndex Partial String Indexing <timeseries.partialindexing>` now works as an exact match, provided that string resolution coincides with index resolution, including a case when both are seconds (:issue:`14826`). See :ref:`Slice vs. Exact Match <timeseries.slice_vs_exact_match>` for details.

.. ipython:: python

  df = DataFrame({'a': [1, 2, 3]}, DatetimeIndex(['2011-12-31 23:59:59',
                                                  '2012-01-01 00:00:00',
                                                  '2012-01-01 00:00:01']))
Previous Behavior:

.. code-block:: ipython

  In [4]: df['2011-12-31 23:59:59']
  Out[4]:
                         a
  2011-12-31 23:59:59  1

  In [5]: df['a']['2011-12-31 23:59:59']
  Out[5]:
  2011-12-31 23:59:59    1
  Name: a, dtype: int64


New Behavior:

.. code-block:: ipython

  In [4]: df['2011-12-31 23:59:59']
  KeyError: '2011-12-31 23:59:59'

  In [5]: df['a']['2011-12-31 23:59:59']
  Out[5]: 1

.. _whatsnew_0200.api_breaking.concat_dtypes:

Concat of different float dtypes will not automatically upcast
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Previously, ``concat`` of multiple objects with different ``float`` dtypes would automatically upcast results to a dtype of ``float64``.
Now the smallest acceptable dtype will be used (:issue:`13247`)

.. ipython:: python

   df1 = pd.DataFrame(np.array([1.0], dtype=np.float32, ndmin=2))
   df1.dtypes

.. ipython:: python

   df2 = pd.DataFrame(np.array([np.nan], dtype=np.float32, ndmin=2))
   df2.dtypes

Previous Behavior:

.. code-block:: ipython

   In [7]: pd.concat([df1,df2]).dtypes
   Out[7]:
   0    float64
   dtype: object

New Behavior:

.. ipython:: python

   pd.concat([df1,df2]).dtypes

.. _whatsnew_0200.api_breaking.gbq:

Pandas Google BigQuery support has moved
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pandas has split off Google BigQuery support into a separate package ``pandas-gbq``. You can ``conda install pandas-gbq -c conda-forge`` or
``pip install pandas-gbq`` to get it. The functionality of :func:`read_gbq` and :meth:`DataFrame.to_gbq` remain the same with the
currently released version of ``pandas-gbq=0.1.4``. Documentation is now hosted `here <https://pandas-gbq.readthedocs.io/>`__  (:issue:`15347`)

.. _whatsnew_0200.api_breaking.memory_usage:

Memory Usage for Index is more Accurate
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In previous versions, showing ``.memory_usage()`` on a pandas structure that has an index, would only include actual index values and not include structures that facilitated fast indexing. This will generally be different for ``Index`` and ``MultiIndex`` and less-so for other index types. (:issue:`15237`)

Previous Behavior:

.. code-block:: ipython

   In [8]: index = Index(['foo', 'bar', 'baz'])

   In [9]: index.memory_usage(deep=True)
   Out[9]: 180

   In [10]: index.get_loc('foo')
   Out[10]: 0

   In [11]: index.memory_usage(deep=True)
   Out[11]: 180

New Behavior:

.. code-block:: ipython

   In [8]: index = Index(['foo', 'bar', 'baz'])

   In [9]: index.memory_usage(deep=True)
   Out[9]: 180

   In [10]: index.get_loc('foo')
   Out[10]: 0

   In [11]: index.memory_usage(deep=True)
   Out[11]: 260

.. _whatsnew_0200.api_breaking.sort_index:

DataFrame.sort_index changes
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In certain cases, calling ``.sort_index()`` on a MultiIndexed DataFrame would return the *same* DataFrame without seeming to sort.
This would happen with a ``lexsorted``, but non-monotonic levels. (:issue:`15622`, :issue:`15687`, :issue:`14015`, :issue:`13431`)

This is *unchanged* from prior versions, but shown for illustration purposes:

.. ipython:: python

    df = DataFrame(np.arange(6), columns=['value'], index=MultiIndex.from_product([list('BA'), range(3)]))
    df

.. ipython:: python

    df.index.is_lexsorted()
    df.index.is_monotonic

Sorting works as expected

.. ipython:: python

    df.sort_index()

.. ipython:: python

    df.sort_index().index.is_lexsorted()
    df.sort_index().index.is_monotonic

However, this example, which has a non-monotonic 2nd level,
doesn't behave as desired.

.. ipython:: python

   df = pd.DataFrame(
           {'value': [1, 2, 3, 4]},
            index=pd.MultiIndex(levels=[['a', 'b'], ['bb', 'aa']],
                                labels=[[0, 0, 1, 1], [0, 1, 0, 1]]))
   df

Previous Behavior:

.. code-block:: python

   In [11]: df.sort_index()
   Out[11]:
         value
   a bb      1
     aa      2
   b bb      3
     aa      4

   In [14]: df.sort_index().index.is_lexsorted()
   Out[14]: True

   In [15]: df.sort_index().index.is_monotonic
   Out[15]: False

New Behavior:

.. ipython:: python

   df.sort_index()
   df.sort_index().index.is_lexsorted()
   df.sort_index().index.is_monotonic


.. _whatsnew_0200.api_breaking.groupby_describe:

Groupby Describe Formatting
^^^^^^^^^^^^^^^^^^^^^^^^^^^

The output formatting of ``groupby.describe()`` now labels the ``describe()`` metrics in the columns instead of the index.
This format is consistent with ``groupby.agg()`` when applying multiple functions at once. (:issue:`4792`)

Previous Behavior:

.. code-block:: ipython

   In [1]: df = pd.DataFrame({'A': [1, 1, 2, 2], 'B': [1, 2, 3, 4]})

   In [2]: df.groupby('A').describe()
   Out[2]:
                   B
   A
   1 count  2.000000
     mean   1.500000
     std    0.707107
     min    1.000000
     25%    1.250000
     50%    1.500000
     75%    1.750000
     max    2.000000
   2 count  2.000000
     mean   3.500000
     std    0.707107
     min    3.000000
     25%    3.250000
     50%    3.500000
     75%    3.750000
     max    4.000000

   In [3]: df.groupby('A').agg([np.mean, np.std, np.min, np.max])
   Out[3]:
        B
     mean       std amin amax
   A
   1  1.5  0.707107    1    2
   2  3.5  0.707107    3    4

New Behavior:

.. ipython:: python

   df = pd.DataFrame({'A': [1, 1, 2, 2], 'B': [1, 2, 3, 4]})

   df.groupby('A').describe()

   df.groupby('A').agg([np.mean, np.std, np.min, np.max])

.. _whatsnew_0200.api_breaking.rolling_pairwise:

Window Binary Corr/Cov operations return a MultiIndex DataFrame
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

A binary window operation, like ``.corr()`` or ``.cov()``, when operating on a ``.rolling(..)``, ``.expanding(..)``, or ``.ewm(..)`` object,
will now return a 2-level ``MultiIndexed DataFrame`` rather than a ``Panel``, as ``Panel`` is now deprecated,
see :ref:`here <whatsnew_0200.api_breaking.deprecate_panel>`. These are equivalent in function,
but a MultiIndexed ``DataFrame`` enjoys more support in pandas.
See the section on :ref:`Windowed Binary Operations <stats.moments.binary>` for more information. (:issue:`15677`)

.. ipython:: python

   np.random.seed(1234)
   df = pd.DataFrame(np.random.rand(100, 2),
                     columns=pd.Index(['A', 'B'], name='bar'),
                     index=pd.date_range('20160101',
                                         periods=100, freq='D', name='foo'))
   df.tail()

Old Behavior:

.. code-block:: ipython

   In [2]: df.rolling(12).corr()
   Out[2]:
   <class 'pandas.core.panel.Panel'>
   Dimensions: 100 (items) x 2 (major_axis) x 2 (minor_axis)
   Items axis: 2016-01-01 00:00:00 to 2016-04-09 00:00:00
   Major_axis axis: A to B
   Minor_axis axis: A to B

New Behavior:

.. ipython:: python

   res = df.rolling(12).corr()
   res.tail()

Retrieving a correlation matrix for a cross-section

.. ipython:: python

   df.rolling(12).corr().loc['2016-04-07']

.. _whatsnew_0200.api_breaking.hdfstore_where:

HDFStore where string comparison
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In previous versions most types could be compared to string column in a ``HDFStore``
usually resulting in an invalid comparsion, returning an empty result frame. These comparisions will now raise a
``TypeError`` (:issue:`15492`)

.. ipython:: python

   df = pd.DataFrame({'unparsed_date': ['2014-01-01', '2014-01-01']})
   df.to_hdf('store.h5', 'key', format='table', data_columns=True)
   df.dtypes

Previous Behavior:

.. code-block:: ipython

   In [4]: pd.read_hdf('store.h5', 'key', where='unparsed_date > ts')
   File "<string>", line 1
     (unparsed_date > 1970-01-01 00:00:01.388552400)
                           ^
   SyntaxError: invalid token

New Behavior:

.. code-block:: ipython

   In [18]: ts = pd.Timestamp('2014-01-01')

   In [19]: pd.read_hdf('store.h5', 'key', where='unparsed_date > ts')
   TypeError: Cannot compare 2014-01-01 00:00:00 of
   type <class 'pandas.tslib.Timestamp'> to string column

.. ipython:: python
   :suppress:

   import os
   os.remove('store.h5')

.. _whatsnew_0200.api_breaking.index_order:

Index.intersection and inner join now preserve the order of the left Index
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

:meth:`Index.intersection` now preserves the order of the calling ``Index`` (left)
instead of the other ``Index`` (right) (:issue:`15582`). This affects the inner
joins, :meth:`DataFrame.join` and :func:`merge`, and the ``.align`` methods.

- ``Index.intersection``

  .. ipython:: python

     left = pd.Index([2, 1, 0])
     left
     right = pd.Index([1, 2, 3])
     right

  Previous Behavior:

  .. code-block:: ipython

     In [4]: left.intersection(right)
     Out[4]: Int64Index([1, 2], dtype='int64')

  New Behavior:

  .. ipython:: python

     left.intersection(right)

- ``DataFrame.join`` and ``pd.merge``

  .. ipython:: python

     left = pd.DataFrame({'a': [20, 10, 0]}, index=[2, 1, 0])
     left
     right = pd.DataFrame({'b': [100, 200, 300]}, index=[1, 2, 3])
     right

  Previous Behavior:

  .. code-block:: ipython

     In [4]: left.join(right, how='inner')
     Out[4]:
         a    b
     1  10  100
     2  20  200

  New Behavior:

  .. ipython:: python

     left.join(right, how='inner')

.. _whatsnew_0200.api_breaking.pivot_table:

Pivot Table always returns a DataFrame
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The documentation for :meth:`pivot_table` states that a ``DataFrame`` is *always* returned. Here a bug
is fixed that allowed this to return a ``Series`` under a narrow circumstance. (:issue:`4386`)

.. ipython:: python

   df = DataFrame({'col1': [3, 4, 5],
                   'col2': ['C', 'D', 'E'],
                   'col3': [1, 3, 9]})
   df

Previous Behavior:

.. code-block:: ipython

   In [2]: df.pivot_table('col1', index=['col3', 'col2'], aggfunc=np.sum)
   Out[2]:
   col3  col2
   1     C       3
   3     D       4
   9     E       5
   Name: col1, dtype: int64

New Behavior:

.. ipython:: python

   df.pivot_table('col1', index=['col3', 'col2'], aggfunc=np.sum)

.. _whatsnew_0200.api:

Other API Changes
^^^^^^^^^^^^^^^^^

- ``numexpr`` version is now required to be >= 2.4.6 and it will not be used at all if this requisite is not fulfilled (:issue:`15213`).
- ``CParserError`` has been renamed to ``ParserError`` in ``pd.read_csv()`` and will be removed in the future (:issue:`12665`)
- ``SparseArray.cumsum()`` and ``SparseSeries.cumsum()`` will now always return ``SparseArray`` and ``SparseSeries`` respectively (:issue:`12855`)
- ``DataFrame.applymap()`` with an empty ``DataFrame`` will return a copy of the empty ``DataFrame`` instead of a ``Series`` (:issue:`8222`)
- ``Series.map()`` now respects default values of dictionary subclasses with a ``__missing__`` method, such as ``collections.Counter`` (:issue:`15999`)
- ``.loc`` has compat with ``.ix`` for accepting iterators, and NamedTuples (:issue:`15120`)
- ``interpolate()`` and ``fillna()`` will raise a ``ValueError`` if the ``limit`` keyword argument is not greater than 0. (:issue:`9217`)
- ``pd.read_csv()`` will now issue a ``ParserWarning`` whenever there are conflicting values provided by the ``dialect`` parameter and the user (:issue:`14898`)
- ``pd.read_csv()`` will now raise a ``ValueError`` for the C engine if the quote character is larger than than one byte (:issue:`11592`)
- ``inplace`` arguments now require a boolean value, else a ``ValueError`` is thrown (:issue:`14189`)
- ``pandas.api.types.is_datetime64_ns_dtype`` will now report ``True`` on a tz-aware dtype, similar to ``pandas.api.types.is_datetime64_any_dtype``
- ``DataFrame.asof()`` will return a null filled ``Series`` instead the scalar ``NaN`` if a match is not found (:issue:`15118`)
- Specific support for ``copy.copy()`` and ``copy.deepcopy()`` functions on NDFrame objects (:issue:`15444`)
- ``Series.sort_values()`` accepts a one element list of bool for consistency with the behavior of ``DataFrame.sort_values()`` (:issue:`15604`)
- ``.merge()`` and ``.join()`` on ``category`` dtype columns will now preserve the category dtype when possible (:issue:`10409`)
- ``SparseDataFrame.default_fill_value`` will be 0, previously was ``nan`` in the return from ``pd.get_dummies(..., sparse=True)`` (:issue:`15594`)
- The default behaviour of ``Series.str.match`` has changed from extracting
  groups to matching the pattern. The extracting behaviour was deprecated
  since pandas version 0.13.0 and can be done with the ``Series.str.extract``
  method (:issue:`5224`). As a consequence, the ``as_indexer`` keyword is
  ignored (no longer needed to specify the new behaviour) and is deprecated.
- ``NaT`` will now correctly report ``False`` for datetimelike boolean operations such as ``is_month_start`` (:issue:`15781`)
- ``NaT`` will now correctly return ``np.nan`` for ``Timedelta`` and ``Period`` accessors such as ``days`` and ``quarter`` (:issue:`15782`)
- ``NaT`` will now returns ``NaT`` for ``tz_localize`` and ``tz_convert``
  methods (:issue:`15830`)
- ``DataFrame`` and ``Panel`` constructors with invalid input will now raise ``ValueError`` rather than ``PandasError``, if called with scalar inputs and not axes (:issue:`15541`)

- ``DataFrame`` and ``Panel`` constructors with invalid input will now raise ``ValueError`` rather than ``pandas.core.common.PandasError``, if called with scalar inputs and not axes; The exception ``PandasError`` is removed as well. (:issue:`15541`)
- The exception ``pandas.core.common.AmbiguousIndexError`` is removed as it is not referenced (:issue:`15541`)

.. _whatsnew_0200.privacy:

Privacy Changes
~~~~~~~~~~~~~~~

.. _whatsnew_0200.privacy.extensions:

Modules Privacy Has Changed
^^^^^^^^^^^^^^^^^^^^^^^^^^^

Some formerly public python/c/c++/cython extension modules have been moved and/or renamed. These are all removed from the public API.
Furthermore, the ``pandas.core``, ``pandas.io``, and ``pandas.util`` top-level modules are now considered to be PRIVATE.
If indicated, a deprecation warning will be issued if you reference theses modules. (:issue:`12588`)

.. csv-table::
    :header: "Previous Location", "New Location", "Deprecated"
    :widths: 30, 30, 4

    "pandas.lib", "pandas._libs.lib", "X"
    "pandas.tslib", "pandas._libs.tslib", "X"
    "pandas.computation", "pandas.core.computation", ""
    "pandas.msgpack", "pandas.io.msgpack", ""
    "pandas.index", "pandas._libs.index", ""
    "pandas.algos", "pandas._libs.algos", ""
    "pandas.hashtable", "pandas._libs.hashtable", ""
    "pandas.indexes", "pandas.core.indexes", ""
    "pandas.json", "pandas.io.json.libjson", "X"
    "pandas.parser", "pandas.io.libparsers", "X"
    "pandas.formats", "pandas.io.formats", ""
    "pandas.sparse", "pandas.core.sparse", ""
    "pandas.tools", "pandas.core.reshape", ""
    "pandas.types", "pandas.core.dtypes", ""
    "pandas.io.sas.saslib", "pandas.io.sas.libsas", ""
    "pandas._join", "pandas._libs.join", ""
    "pandas._hash", "pandas.tools.libhash", ""
    "pandas._period", "pandas._libs.period", ""
    "pandas._sparse", "pandas.core.sparse.libsparse", ""
    "pandas._testing", "pandas.util.libtesting", ""
    "pandas._window", "pandas.core.libwindow", ""

- The function :func:`~pandas.api.types.union_categoricals` is now importable from ``pandas.api.types``, formerly from ``pandas.types.concat`` (:issue:`15998`)

.. _whatsnew_0200.privacy.deprecate_plotting:

Deprecate .plotting
^^^^^^^^^^^^^^^^^^^

The ``pandas.tools.plotting`` module has been deprecated,  in favor of the top level ``pandas.plotting`` module. All the public plotting functions are now available
from ``pandas.plotting`` (:issue:`12548`).

Furthermore, the top-level ``pandas.scatter_matrix`` and ``pandas.plot_params`` are deprecated.
Users can import these from ``pandas.plotting`` as well.

Previous script:

.. code-block:: python

   pd.tools.plotting.scatter_matrix(df)
   pd.scatter_matrix(df)

Should be changed to:

.. code-block:: python

    pd.plotting.scatter_matrix(df)


.. _whatsnew_0200.privacy.development:

Other Developement Changes
^^^^^^^^^^^^^^^^^^^^^^^^^^

- Building pandas for development now requires ``cython >= 0.23`` (:issue:`14831`)
- Require at least 0.23 version of cython to avoid problems with character encodings (:issue:`14699`)
- Reorganization of timeseries tests (:issue:`14854`)
- Reorganization of date converter tests (:issue:`15707`)

.. _whatsnew_0200.deprecations:

Deprecations
~~~~~~~~~~~~

- ``SparseArray.to_dense()`` has deprecated the ``fill`` parameter, as that parameter was not being respected (:issue:`14647`)
- ``SparseSeries.to_dense()`` has deprecated the ``sparse_only`` parameter (:issue:`14647`)
- ``Series.repeat()`` has deprecated the ``reps`` parameter in favor of ``repeats`` (:issue:`12662`)
- The ``Series`` constructor and ``.astype`` method have deprecated accepting timestamp dtypes without a frequency (e.g. ``np.datetime64``) for the ``dtype`` parameter (:issue:`15524`)
- ``Index.repeat()`` and ``MultiIndex.repeat()`` have deprecated the ``n`` parameter in favor of ``repeats`` (:issue:`12662`)
- ``Categorical.searchsorted()`` and ``Series.searchsorted()`` have deprecated the ``v`` parameter in favor of ``value`` (:issue:`12662`)
- ``TimedeltaIndex.searchsorted()``, ``DatetimeIndex.searchsorted()``, and ``PeriodIndex.searchsorted()`` have deprecated the ``key`` parameter in favor of ``value`` (:issue:`12662`)
- ``DataFrame.astype()`` has deprecated the ``raise_on_error`` parameter in favor of ``errors`` (:issue:`14878`)
- ``Series.sortlevel`` and ``DataFrame.sortlevel`` have been deprecated in favor of ``Series.sort_index`` and ``DataFrame.sort_index`` (:issue:`15099`)
- importing ``concat`` from ``pandas.tools.merge`` has been deprecated in favor of imports from the ``pandas`` namespace. This should only affect explict imports (:issue:`15358`)
- ``Series/DataFrame/Panel.consolidate()`` been deprecated as a public method. (:issue:`15483`)
- The ``as_indexer`` keyword of ``Series.str.match()`` has been deprecated (ignored keyword) (:issue:`15257`).
- The following top-level pandas functions have been deprecated and will be removed in a future version (:issue:`13790`, :issue:`15940`)

  * ``pd.pnow()``, replaced by ``Period.now()``
  * ``pd.Term``, is removed, as it is not applicable to user code. Instead use in-line string expressions in the where clause when searching in HDFStore
  * ``pd.Expr``, is removed, as it is not applicable to user code.
  * ``pd.match()``, is removed.
  * ``pd.groupby()``, replaced by using the ``.groupby()`` method directly on a ``Series/DataFrame``
  * ``pd.get_store()``, replaced by a direct call to ``pd.HDFStore(...)``

.. _whatsnew_0200.prior_deprecations:

Removal of prior version deprecations/changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- The ``pandas.rpy`` module is removed. Similar functionality can be accessed
  through the `rpy2 <https://rpy2.readthedocs.io/>`__ project.
  See the :ref:`R interfacing docs <rpy>` for more details.
- The ``pandas.io.ga`` module with a ``google-analytics`` interface is removed (:issue:`11308`).
  Similar functionality can be found in the `Google2Pandas <https://github.com/panalysis/Google2Pandas>`__ package.
- ``pd.to_datetime`` and ``pd.to_timedelta`` have dropped the ``coerce`` parameter in favor of ``errors`` (:issue:`13602`)
- ``pandas.stats.fama_macbeth``, ``pandas.stats.ols``, ``pandas.stats.plm`` and ``pandas.stats.var``, as well as the top-level ``pandas.fama_macbeth`` and ``pandas.ols`` routines are removed. Similar functionaility can be found in the `statsmodels <shttp://www.statsmodels.org/dev/>`__ package. (:issue:`11898`)
- The ``TimeSeries`` and ``SparseTimeSeries`` classes, aliases of ``Series``
  and ``SparseSeries``, are removed (:issue:`10890`, :issue:`15098`).
- ``Series.is_time_series`` is dropped in favor of ``Series.index.is_all_dates`` (:issue:`15098`)
- The deprecated ``irow``, ``icol``, ``iget`` and ``iget_value`` methods are removed
  in favor of ``iloc`` and ``iat`` as explained :ref:`here <whatsnew_0170.deprecations>` (:issue:`10711`).
- The deprecated ``DataFrame.iterkv()`` has been removed in favor of ``DataFrame.iteritems()`` (:issue:`10711`)
- The ``Categorical`` constructor has dropped the ``name`` parameter (:issue:`10632`)
- ``Categorical`` has dropped support for ``NaN`` categories (:issue:`10748`)
- The ``take_last`` parameter has been dropped from ``duplicated()``, ``drop_duplicates()``, ``nlargest()``, and ``nsmallest()`` methods (:issue:`10236`, :issue:`10792`, :issue:`10920`)
- ``Series``, ``Index``, and ``DataFrame`` have dropped the ``sort`` and ``order`` methods (:issue:`10726`)
- Where clauses in ``pytables`` are only accepted as strings and expressions types and not other data-types (:issue:`12027`)
- ``DataFrame`` has dropped the ``combineAdd`` and ``combineMult`` methods in favor of ``add`` and ``mul`` respectively (:issue:`10735`)

.. _whatsnew_0200.performance:

Performance Improvements
~~~~~~~~~~~~~~~~~~~~~~~~

- Improved performance of ``pd.wide_to_long()`` (:issue:`14779`)
- Improved performance of ``pd.factorize()`` by releasing the GIL with ``object`` dtype when inferred as strings (:issue:`14859`, :issue:`16057`)
- Improved performance of timeseries plotting with an irregular DatetimeIndex
  (or with ``compat_x=True``) (:issue:`15073`).
- Improved performance of ``groupby().cummin()`` and ``groupby().cummax()`` (:issue:`15048`, :issue:`15109`, :issue:`15561`, :issue:`15635`)
- Improved performance and reduced memory when indexing with a ``MultiIndex`` (:issue:`15245`)
- When reading buffer object in ``read_sas()`` method without specified format, filepath string is inferred rather than buffer object. (:issue:`14947`)
- Improved performance of ``.rank()`` for categorical data (:issue:`15498`)
- Improved performance when using ``.unstack()`` (:issue:`15503`)
- Improved performance of merge/join on ``category`` columns (:issue:`10409`)
- Improved performance of ``drop_duplicates()`` on ``bool`` columns (:issue:`12963`)
- Improve performance of ``pd.core.groupby.GroupBy.apply`` when the applied
  function used the ``.name`` attribute of the group DataFrame (:issue:`15062`).
- Improved performance of ``iloc`` indexing with a list or array (:issue:`15504`).
- Improved performance of ``Series.sort_index()`` with a monotonic index (:issue:`15694`)
- Improved performance in ``pd.read_csv()`` on some platforms with buffered reads (:issue:`16039`)

.. _whatsnew_0200.bug_fixes:

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 ``Timestamp`` incorrectly localizing timezones during construction (:issue:`11481`, :issue:`15777`)
- 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`)
- Cleaned up ``PeriodIndex`` constructor, including raising on floats more consistently (:issue:`13277`)
- Bug in using ``__deepcopy__`` on empty NDFrame objects (:issue:`15370`)
- 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 ``DataFrame`` construction with nulls and datetimes in a list-like (:issue:`15869`)
- Bug in ``DataFrame.fillna()`` with tz-aware datetimes (:issue:`15855`)
- Bug in ``is_string_dtype``, ``is_timedelta64_ns_dtype``, and ``is_string_like_dtype`` in which an error was raised when ``None`` was passed in (:issue:`15941`)
- Bug in the return type of ``pd.unique`` on a ``Categorical``, which was returning an ndarray and not a ``Categorical`` (:issue:`15903`)
- Bug in ``Index.to_series()`` where the index was not copied (and so mutating later would change the original), (:issue:`15949`)

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 ``.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 ``pd.concat()`` where the names of ``MultiIndex`` of resulting ``DataFrame`` are not handled correctly when ``None`` is presented in the names of ``MultiIndex`` of input ``DataFrame`` (:issue:`15787`)
- Bug in ``DataFrame.sort_index()`` and ``Series.sort_index()`` where ``na_position`` doesn't work with a ``MultiIndex`` (:issue:`14784`)

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`)
- Bug in ``pd.read_csv()`` when an index was specified and no values were specified as null values (:issue:`15835`)
- Bug in ``pd.read_csv()`` in which certain invalid file objects caused the Python interpreter to crash (:issue:`15337`)
- Bug in ``pd.read_csv()`` in which invalid values for ``nrows`` and ``chunksize`` were allowed (:issue:`15767`)
- Bug in ``pd.read_csv()`` for the Python engine in which unhelpful error messages were being raised when parsing errors occurred (:issue:`15910`)
- Bug in ``pd.read_csv()`` in which the ``skipfooter`` parameter was not being properly validated (:issue:`15925`)
- Bug in ``pd.to_csv()`` in which there was numeric overflow when a timestamp index was being written (:issue:`15982`)
- 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 ``.to_json()`` for the C engine where rollover was not correctly handled for case where frac is odd and diff is exactly 0.5 (:issue:`15716`, :issue:`15864`)
- Bug in ``pd.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`)
- Bug in the ``Series`` repr not showing the length when the output was truncated (:issue:`15962`).

Plotting
^^^^^^^^

- 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 the date and time converters pandas registers with matplotlib not handling multiple dimensions (:issue:`16026`)
- Bug in ``pd.scatter_matrix()`` could accept either ``color`` or ``c``, but not both (:issue:`14855`)

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 ``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`)

Sparse
^^^^^^

- 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`)
- Bug in sparse array indexing in which indices were not being validated (:issue:`15863`)

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.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 with ``sort=True`` in ``DataFrame.join`` and ``pd.merge`` when joining on indexes (:issue:`15582`)
- Bug in ``DataFrame.nsmallest`` and ``DataFrame.nlargest`` where identical values resulted in duplicated rows (:issue:`15297`)

Numeric
^^^^^^^

- 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 ``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`)

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`)
- 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`)