.. _whatsnew_0131:

v0.13.1 (February 3, 2014)
--------------------------

This is a minor release from 0.13.0 and includes a small number of API changes, several 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:

- Added ``infer_datetime_format`` keyword to ``read_csv/to_datetime`` to allow speedups for homogeneously formatted datetimes.
- Will intelligently limit display precision for datetime/timedelta formats.
- Enhanced Panel :meth:`~pandas.Panel.apply` method.
- Suggested tutorials in new :ref:`Tutorials<tutorials>` section.
- Our pandas ecosystem is growing, We now feature related projects in a new :ref:`Pandas Ecosystem<ecosystem>` section.
- Much work has been taking place on improving the docs, and a new :ref:`Contributing<contributing>` section has been added.
- Even though it may only be of interest to devs, we <3 our new CI status page: `ScatterCI <http://scatterci.github.io/pydata/pandas>`__.

.. warning::

   0.13.1 fixes a bug that was caused by a combination of having numpy < 1.8, and doing
   chained assignment on a string-like array. Please review :ref:`the docs<indexing.view_versus_copy>`,
   chained indexing can have unexpected results and should generally be avoided.

   This would previously segfault:

   .. ipython:: python

      df = DataFrame(dict(A = np.array(['foo','bar','bah','foo','bar'])))
      df['A'].iloc[0] = np.nan
      df

   The recommended way to do this type of assignment is:

   .. ipython:: python

      df = DataFrame(dict(A = np.array(['foo','bar','bah','foo','bar'])))
      df.ix[0,'A'] = np.nan
      df

Output Formatting Enhancements
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- df.info() view now display dtype info per column (:issue:`5682`)

- df.info() now honors the option ``max_info_rows``, to disable null counts for large frames (:issue:`5974`)

  .. ipython:: python

     max_info_rows = pd.get_option('max_info_rows')

     df = DataFrame(dict(A = np.random.randn(10),
                         B = np.random.randn(10),
                         C = date_range('20130101',periods=10)))
     df.iloc[3:6,[0,2]] = np.nan

  .. ipython:: python

     # set to not display the null counts
     pd.set_option('max_info_rows',0)
     df.info()

  .. ipython:: python

     # this is the default (same as in 0.13.0)
     pd.set_option('max_info_rows',max_info_rows)
     df.info()

- Add ``show_dimensions`` display option for the new DataFrame repr to control whether the dimensions print.

  .. ipython:: python

      df = DataFrame([[1, 2], [3, 4]])
      pd.set_option('show_dimensions', False)
      df

      pd.set_option('show_dimensions', True)
      df

- The ``ArrayFormatter`` for ``datetime`` and ``timedelta64`` now intelligently
  limit precision based on the values in the array (:issue:`3401`)

  Previously output might look like:

  .. code-block:: python

        age                 today               diff
      0 2001-01-01 00:00:00 2013-04-19 00:00:00 4491 days, 00:00:00
      1 2004-06-01 00:00:00 2013-04-19 00:00:00 3244 days, 00:00:00

  Now the output looks like:

  .. ipython:: python

     df = DataFrame([ Timestamp('20010101'),
                      Timestamp('20040601') ], columns=['age'])
     df['today'] = Timestamp('20130419')
     df['diff'] = df['today']-df['age']
     df

API changes
~~~~~~~~~~~

- Add ``-NaN`` and ``-nan`` to the default set of NA values (:issue:`5952`).
  See :ref:`NA Values <io.na_values>`.

- Added ``Series.str.get_dummies`` vectorized string method (:issue:`6021`), to extract
  dummy/indicator variables for separated string columns:

  .. ipython:: python

      s = Series(['a', 'a|b', np.nan, 'a|c'])
      s.str.get_dummies(sep='|')

- Added the ``NDFrame.equals()`` method to compare if two NDFrames are
  equal have equal axes, dtypes, and values. Added the
  ``array_equivalent`` function to compare if two ndarrays are
  equal. NaNs in identical locations are treated as
  equal. (:issue:`5283`) See also :ref:`the docs<basics.equals>` for a motivating example.

  .. ipython:: python
      :okwarning:
      
      df = DataFrame({'col':['foo', 0, np.nan]})
      df2 = DataFrame({'col':[np.nan, 0, 'foo']}, index=[2,1,0])
      df.equals(df2)
      df.equals(df2.sort())

      import pandas.core.common as com
      com.array_equivalent(np.array([0, np.nan]), np.array([0, np.nan]))
      np.array_equal(np.array([0, np.nan]), np.array([0, np.nan]))

- ``DataFrame.apply`` will use the ``reduce`` argument to determine whether a
  ``Series`` or a ``DataFrame`` should be returned when the ``DataFrame`` is
  empty (:issue:`6007`).

  Previously, calling ``DataFrame.apply`` an empty ``DataFrame`` would return
  either a ``DataFrame`` if there were no columns, or the function being
  applied would be called with an empty ``Series`` to guess whether a
  ``Series`` or ``DataFrame`` should be returned:

  .. ipython:: python

     def applied_func(col):
        print("Apply function being called with: ", col)
        return col.sum()

     empty = DataFrame(columns=['a', 'b'])
     empty.apply(applied_func)

  Now, when ``apply`` is called on an empty ``DataFrame``: if the ``reduce``
  argument is ``True`` a ``Series`` will returned, if it is ``False`` a
  ``DataFrame`` will be returned, and if it is ``None`` (the default) the
  function being applied will be called with an empty series to try and guess
  the return type.

  .. ipython:: python

     empty.apply(applied_func, reduce=True)
     empty.apply(applied_func, reduce=False)

Prior Version Deprecations/Changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There are no announced changes in 0.13 or prior that are taking effect as of 0.13.1

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

There are no deprecations of prior behavior in 0.13.1

Enhancements
~~~~~~~~~~~~

- ``pd.read_csv`` and ``pd.to_datetime`` learned a new ``infer_datetime_format`` keyword which greatly
  improves parsing perf in many cases. Thanks to @lexual for suggesting and @danbirken
  for rapidly implementing. (:issue:`5490`, :issue:`6021`)

  If ``parse_dates`` is enabled and this flag is set, pandas will attempt to
  infer the format of the datetime strings in the columns, and if it can
  be inferred, switch to a faster method of parsing them.  In some cases
  this can increase the parsing speed by ~5-10x.

  .. code-block:: python

      # Try to infer the format for the index column
      df = pd.read_csv('foo.csv', index_col=0, parse_dates=True,
                       infer_datetime_format=True)

- ``date_format`` and ``datetime_format`` keywords can now be specified when writing to ``excel``
  files (:issue:`4133`)

- ``MultiIndex.from_product`` convenience function for creating a MultiIndex from
  the cartesian product of a set of iterables (:issue:`6055`):

  .. ipython:: python

      shades = ['light', 'dark']
      colors = ['red', 'green', 'blue']

      MultiIndex.from_product([shades, colors], names=['shade', 'color'])

- Panel :meth:`~pandas.Panel.apply` will work on non-ufuncs. See :ref:`the docs<basics.apply_panel>`.

  .. ipython:: python

     import pandas.util.testing as tm
     panel = tm.makePanel(5)
     panel
     panel['ItemA']

  Specifying an ``apply`` that operates on a Series (to return a single element)

  .. ipython:: python

     panel.apply(lambda x: x.dtype, axis='items')

  A similar reduction type operation

  .. ipython:: python

     panel.apply(lambda x: x.sum(), axis='major_axis')

  This is equivalent to

  .. ipython:: python

     panel.sum('major_axis')

  A transformation operation that returns a Panel, but is computing
  the z-score across the major_axis

  .. ipython:: python

     result = panel.apply(
                lambda x: (x-x.mean())/x.std(),
                axis='major_axis')
     result
     result['ItemA']

- Panel :meth:`~pandas.Panel.apply` operating on cross-sectional slabs. (:issue:`1148`)

  .. ipython:: python

     f = lambda x: ((x.T-x.mean(1))/x.std(1)).T

     result = panel.apply(f, axis = ['items','major_axis'])
     result
     result.loc[:,:,'ItemA']

  This is equivalent to the following

  .. ipython:: python

     result = Panel(dict([ (ax,f(panel.loc[:,:,ax]))
                             for ax in panel.minor_axis ]))
     result
     result.loc[:,:,'ItemA']

Performance
~~~~~~~~~~~

Performance improvements for 0.13.1

- Series datetime/timedelta binary operations (:issue:`5801`)
- DataFrame ``count/dropna`` for ``axis=1``
- Series.str.contains now has a `regex=False` keyword which can be faster for plain (non-regex) string patterns. (:issue:`5879`)
- Series.str.extract (:issue:`5944`)
- ``dtypes/ftypes`` methods (:issue:`5968`)
- indexing with object dtypes (:issue:`5968`)
- ``DataFrame.apply`` (:issue:`6013`)
- Regression in JSON IO (:issue:`5765`)
- Index construction from Series (:issue:`6150`)

Experimental
~~~~~~~~~~~~

There are no experimental changes in 0.13.1

Bug Fixes
~~~~~~~~~

See :ref:`V0.13.1 Bug Fixes<release.bug_fixes-0.13.1>` for an extensive list of bugs that have been fixed in 0.13.1.

See the :ref:`full release notes
<release>` or issue tracker
on GitHub for a complete list of all API changes, Enhancements and Bug Fixes.