v0.14.0.txt

.. _whatsnew_0140:

v0.14.0 (May ? , 2014)
----------------------

This is a major release from 0.13.1 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:

- MultIndexing Using Slicers
- Joining a singly-indexed DataFrame with a multi-indexed DataFrame
- More consistency in groupby results and more flexible groupby specifications

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

- ``read_excel`` uses 0 as the default sheet (:issue:`6573`)
- ``iloc`` will now accept out-of-bounds indexers for slices, e.g. a value that exceeds the length of the object being
  indexed. These will be excluded. This will make pandas conform more with python/numpy indexing of out-of-bounds
  values. A single indexer / list of indexers that is out-of-bounds will still raise
  ``IndexError`` (:issue:`6296`, :issue:`6299`). This could result in an empty axis (e.g. an empty DataFrame being returned)

  .. ipython:: python

     dfl = DataFrame(np.random.randn(5,2),columns=list('AB'))
     dfl
     dfl.iloc[:,2:3]
     dfl.iloc[:,1:3]
     dfl.iloc[4:6]

  These are out-of-bounds selections

  .. code-block:: python

     dfl.iloc[[4,5,6]]
     IndexError: positional indexers are out-of-bounds

     dfl.iloc[:,4]
     IndexError: single positional indexer is out-of-bounds


- The ``DataFrame.interpolate()`` ``downcast`` keyword default has been changed from ``infer`` to
  ``None``. This is to preseve the original dtype unless explicitly requested otherwise (:issue:`6290`).
- When converting a dataframe to HTML it used to return `Empty DataFrame`. This special case has
  been removed, instead a header with the column names is returned (:issue:`6062`).
- allow a Series to utilize index methods depending on its index type, e.g. ``Series.year`` is now defined
  for a Series with a ``DatetimeIndex`` or a ``PeriodIndex``; trying this on a non-supported Index type will
  now raise a ``TypeError``. (:issue:`4551`, :issue:`4056`, :issue:`5519`)

  The following affected:

  - ``date,time,year,month,day``
  - ``hour,minute,second,weekofyear``
  - ``week,dayofweek,dayofyear,quarter``
  - ``microsecond,nanosecond,qyear``
  - ``min(),max()``
  - ``pd.infer_freq()``

  .. ipython:: python

     s = Series(np.random.randn(5),index=tm.makeDateIndex(5))
     s
     s.year
     s.index.year

- More consistent behaviour for some groupby methods:

  groupby ``head`` and ``tail`` now act more like ``filter`` rather than an aggregation:

  .. ipython:: python

     df = pd.DataFrame([[1, 2], [1, 4], [5, 6]], columns=['A', 'B'])
     g = df.groupby('A')
     g.head(1)  # filters DataFrame

     g.apply(lambda x: x.head(1))  # used to simply fall-through

  groupby head and tail respect column selection:

  .. ipython:: python

     g[['B']].head(1)

  groupby ``nth`` now filters by default, with optional dropna argument to ignore
  NaN (to replicate the previous behaviour.), See :ref:`the docs <groupby.nth>`.

  .. ipython:: python

     DataFrame([[1, np.nan], [1, 4], [5, 6]], columns=['A', 'B'])
     g = df.groupby('A')
     g.nth(0)  # can also use negative ints

     g.nth(0, dropna='any')  # similar to old behaviour

- Allow specification of a more complex groupby via ``pd.Grouper``, such as grouping
  by a Time and a string field simultaneously. See :ref:`the docs <groupby.specify>`. (:issue:`3794`)

- Local variable usage has changed in
  :func:`pandas.eval`/:meth:`DataFrame.eval`/:meth:`DataFrame.query`
  (:issue:`5987`). For the :class:`~pandas.DataFrame` methods, two things have
  changed

  - Column names are now given precedence over locals
  - Local variables must be referred to explicitly. This means that even if
    you have a local variable that is *not* a column you must still refer to
    it with the ``'@'`` prefix.
  - You can have an expression like ``df.query('@a < a')`` with no complaints
    from ``pandas`` about ambiguity of the name ``a``.
  - The top-level :func:`pandas.eval` function does not allow you use the
    ``'@'`` prefix and provides you with an error message telling you so.
  - ``NameResolutionError`` was removed because it isn't necessary anymore.

- ``concat`` will now concatenate mixed Series and DataFrames using the Series name
  or numbering columns as needed (:issue:`2385`). See :ref:`the docs <merging.mixed_ndims>`
- Slicing and advanced/boolean indexing operations on ``Index`` classes will no
  longer change type of the resulting index (:issue:`6440`)

  .. ipython:: python

     i = pd.Index([1, 2, 3, 'a' , 'b', 'c'])
     i[[0,1,2]]

  Previously, the above operation would return ``Int64Index``.  If you'd like
  to do this manually, use :meth:`Index.astype`

  .. ipython:: python

     i[[0,1,2]].astype(np.int_)

- ``set_index`` no longer converts MultiIndexes to an Index of tuples. For example,
  the old behavior returned an Index in this case (:issue:`6459`):

  .. ipython:: python
     :suppress:

     from itertools import product
     tuples = list(product(('a', 'b'), ('c', 'd')))
     mi = MultiIndex.from_tuples(tuples)
     df_multi = DataFrame(np.random.randn(4, 2), index=mi)
     tuple_ind = pd.Index(tuples)

  .. ipython:: python

     df_multi.index

     @suppress
     df_multi.index = tuple_ind

     # Old behavior, casted MultiIndex to an Index
     df_multi.set_index(df_multi.index)

     @suppress
     df_multi.index = mi

     # New behavior
     df_multi.set_index(df_multi.index)

  This also applies when passing multiple indices to ``set_index``:

  .. ipython:: python

    @suppress
    df_multi.index = tuple_ind

    # Old output, 2-level MultiIndex of tuples
    df_multi.set_index([df_multi.index, df_multi.index])

    @suppress
    df_multi.index = mi

    # New output, 4-level MultiIndex
    df_multi.set_index([df_multi.index, df_multi.index])

- Following keywords are now acceptable for :meth:`DataFrame.plot(kind='bar')` and :meth:`DataFrame.plot(kind='barh')`.

  - `width`: Specify the bar width. In previous versions, static value 0.5 was passed to matplotlib and it cannot be overwritten. (:issue:`6604`)

  - `align`: Specify the bar alignment. Default is `center` (different from matplotlib). In previous versions, pandas passes `align='edge'` to matplotlib and adjust the location to `center` by itself, and it results `align` keyword is not applied as expected. (:issue:`4525`)

  - `position`: Specify relative alignments for bar plot layout. From 0 (left/bottom-end) to 1(right/top-end). Default is 0.5 (center). (:issue:`6604`)

  Because of the default `align` value changes, coordinates of bar plots are now located on integer values (0.0, 1.0, 2.0 ...). This is intended to make bar plot be located on the same coodinates as line plot. However, bar plot may differs unexpectedly when you manually adjust the bar location or drawing area, such as using `set_xlim`, `set_ylim`, etc. In this cases, please modify your script to meet with new coordinates.

- ``pairwise`` keyword was added to the statistical moment functions
  ``rolling_cov``, ``rolling_corr``, ``ewmcov``, ``ewmcorr``,
  ``expanding_cov``, ``expanding_corr`` to allow the calculation of moving
  window covariance and correlation matrices (:issue:`4950`). See
  :ref:`Computing rolling pairwise covariances and correlations
  <stats.moments.corr_pairwise>` in the docs.

  .. ipython:: python

    df = DataFrame(np.random.randn(10,4),columns=list('ABCD'))
    covs = rolling_cov(df[['A','B','C']], df[['B','C','D']], 5, pairwise=True)
    covs[df.index[-1]]

- ``Series.iteritems()`` is now lazy (returns an iterator rather than a list). This was the documented behavior prior to 0.14. (:issue:`6760`)
- ``Panel.shift`` now uses ``NDFrame.shift``. It no longer drops the ``nan`` data and retains its original shape.  (:issue:`4867`)


MultiIndexing Using Slicers
~~~~~~~~~~~~~~~~~~~~~~~~~~~

In 0.14.0 we added a new way to slice multi-indexed objects.
You can slice a multi-index by providing multiple indexers.

You can provide any of the selectors as if you are indexing by label, see :ref:`Selection by Label <indexing.label>`,
including slices, lists of labels, labels, and boolean indexers.

You can use ``slice(None)`` to select all the contents of *that* level. You do not need to specify all the
*deeper* levels, they will be implied as ``slice(None)``.

As usual, **both sides** of the slicers are included as this is label indexing.

See :ref:`the docs<indexing.mi_slicers>`
See also issues (:issue:`6134`, :issue:`4036`, :issue:`3057`, :issue:`2598`, :issue:`5641`)

.. warning::

   You should specify all axes in the ``.loc`` specifier, meaning the indexer for the **index** and
   for the **columns**. Their are some ambiguous cases where the passed indexer could be mis-interpreted
   as indexing *both* axes, rather than into say the MuliIndex for the rows.

   You should do this:

   .. code-block:: python

      df.loc[(slice('A1','A3'),.....),:]

   rather than this:

   .. code-block:: python

      df.loc[(slice('A1','A3'),.....)]

.. warning::

   You will need to make sure that the selection axes are fully lexsorted!

.. ipython:: python

   def mklbl(prefix,n):
       return ["%s%s" % (prefix,i)  for i in range(n)]

   index = MultiIndex.from_product([mklbl('A',4),
                                    mklbl('B',2),
                                    mklbl('C',4),
                                    mklbl('D',2)])
   columns = MultiIndex.from_tuples([('a','foo'),('a','bar'),
                                     ('b','foo'),('b','bah')],
                                      names=['lvl0', 'lvl1'])
   df = DataFrame(np.arange(len(index)*len(columns)).reshape((len(index),len(columns))),
                  index=index,
                  columns=columns).sortlevel().sortlevel(axis=1)
   df

Basic multi-index slicing using slices, lists, and labels.

.. ipython:: python

   df.loc[(slice('A1','A3'),slice(None), ['C1','C3']),:]

You can use a ``pd.IndexSlice`` to shortcut the creation of these slices

.. ipython:: python

   idx = pd.IndexSlice
   df.loc[idx[:,:,['C1','C3']],idx[:,'foo']]

It is possible to perform quite complicated selections using this method on multiple
axes at the same time.

.. ipython:: python

   df.loc['A1',(slice(None),'foo')]
   df.loc[idx[:,:,['C1','C3']],idx[:,'foo']]

Using a boolean indexer you can provide selection related to the *values*.

.. ipython:: python

   mask = df[('a','foo')]>200
   df.loc[idx[mask,:,['C1','C3']],idx[:,'foo']]

You can also specify the ``axis`` argument to ``.loc`` to interpret the passed
slicers on a single axis.

.. ipython:: python

   df.loc(axis=0)[:,:,['C1','C3']]

Furthermore you can *set* the values using these methods

.. ipython:: python

   df2 = df.copy()
   df2.loc(axis=0)[:,:,['C1','C3']] = -10
   df2

You can use a right-hand-side of an alignable object as well.

.. ipython:: python

   df2 = df.copy()
   df2.loc[idx[:,:,['C1','C3']],:] = df2*1000
   df2

Plotting With Errorbars
~~~~~~~~~~~~~~~~~~~~~~~

Plotting with error bars is now supported in the ``.plot`` method of ``DataFrame`` and ``Series`` objects (:issue:`3796`).

x and y errorbars are supported and can be supplied using the ``xerr`` and ``yerr`` keyword arguments to ``.plot()`` The error values can be specified using a variety of formats.

- As a ``DataFrame`` or ``dict`` of errors with one or more of the column names (or dictionary keys) matching one or more of the column names of the plotting ``DataFrame`` or matching the ``name`` attribute of the ``Series``
- As a ``str`` indicating which of the columns of plotting ``DataFrame`` contain the error values
- As raw values (``list``, ``tuple``, or ``np.ndarray``). Must be the same length as the plotting ``DataFrame``/``Series``

Asymmetrical error bars are also supported, however raw error values must be provided in this case. For a ``M`` length ``Series``, a ``Mx2`` array should be provided indicating lower and upper (or left and right) errors. For a ``MxN`` ``DataFrame``, asymmetrical errors should be in a ``Mx2xN`` array.


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

Therse are prior version deprecations that are taking effect as of 0.14.0.

- Remove ``column`` keyword from ``DataFrame.sort`` (:issue:`4370`)

- Remove ``precision`` keyword from :func:`set_eng_float_format` (:issue:`6641`)

- Remove ``force_unicode`` keyword from :meth:`DataFrame.to_string`,
  :meth:`DataFrame.to_latex`, and :meth:`DataFrame.to_html`; these function
  encode in unicode by default (:issue:`6641`)

- Remove ``nanRep`` keyword from :meth:`DataFrame.to_csv` and
  :meth:`DataFrame.to_string` (:issue:`6641`)

- Remove ``unique`` keyword from :meth:`HDFStore.select_column` (:issue:`6641`)

- Remove ``inferTimeRule`` keyword from :func:`Timestamp.offset` (:issue:`6641`)

- Remove ``name`` keyword from :func:`get_data_yahoo` and
  :func:`get_data_google` (:issue:`6641`)

- Remove ``offset`` keyword from :class:`DatetimeIndex` constructor
  (:issue:`6641`)

- Remove ``time_rule`` from several rolling-moment statistical functions, such
  as :func:`rolling_sum` (:issue:`6641`)
  

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

- The :func:`pivot_table`/:meth:`DataFrame.pivot_table` and :func:`crosstab` functions
  now take arguments ``index`` and ``columns`` instead of ``rows`` and ``cols``.  A
  ``FutureWarning`` is raised  to alert that the old ``rows`` and ``cols`` arguments
  will not be supported in a future release (:issue:`5505`)

- The :meth:`DataFrame.drop_duplicates` and :meth:`DataFrame.duplicated` methods
  now take argument ``subset`` instead of ``cols`` to better align with
  :meth:`DataFrame.dropna`.  A ``FutureWarning`` is raised  to alert that the old
  ``cols`` arguments will not be supported in a future release (:issue:`6680`)

- The :meth:`DataFrame.to_csv` and :meth:`DataFrame.to_excel` functions
  now takes argument ``columns`` instead of ``cols``.  A
  ``FutureWarning`` is raised  to alert that the old ``cols`` arguments
  will not be supported in a future release (:issue:`6645`)

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

- ``DataFrame.to_latex`` now takes a longtable keyword, which if True will return a table in a longtable environment. (:issue:`6617`)
- ``pd.read_clipboard`` will, if 'sep' is unspecified, try to detect data copied from a spreadsheet
  and parse accordingly. (:issue:`6223`)
- ``plot(legend='reverse')`` will now reverse the order of legend labels for
  most plot kinds. (:issue:`6014`)
- Hexagonal bin plots from ``DataFrame.plot`` with ``kind='hexbin'`` (:issue:`5478`)
- Joining a singly-indexed DataFrame with a multi-indexed DataFrame (:issue:`3662`)

  See :ref:`the docs<merging.join_on_mi>`. Joining multi-index DataFrames on both the left and right is not yet supported ATM.

  .. ipython:: python

     household = DataFrame(dict(household_id = [1,2,3],
                                male = [0,1,0],
                                wealth = [196087.3,316478.7,294750]),
                           columns = ['household_id','male','wealth']
                          ).set_index('household_id')
     household
     portfolio = DataFrame(dict(household_id = [1,2,2,3,3,3,4],
                                asset_id = ["nl0000301109","nl0000289783","gb00b03mlx29",
                                            "gb00b03mlx29","lu0197800237","nl0000289965",np.nan],
                                name = ["ABN Amro","Robeco","Royal Dutch Shell","Royal Dutch Shell",
                                        "AAB Eastern Europe Equity Fund","Postbank BioTech Fonds",np.nan],
                                share = [1.0,0.4,0.6,0.15,0.6,0.25,1.0]),
                           columns = ['household_id','asset_id','name','share']
                          ).set_index(['household_id','asset_id'])
     portfolio

     household.join(portfolio, how='inner')

- ``quotechar``, ``doublequote``, and ``escapechar`` can now be specified when
  using ``DataFrame.to_csv`` (:issue:`5414`, :issue:`4528`)
- Added a ``to_julian_date`` function to ``TimeStamp`` and ``DatetimeIndex``
  to convert to the Julian Date used primarily in astronomy. (:issue:`4041`)
- ``DataFrame.to_stata`` will now check data for compatibility with Stata data types
  and will upcast when needed.  When it isn't possibly to losslessly upcast, a warning
  is raised (:issue:`6327`)
- ``DataFrame.to_stata`` and ``StataWriter`` will accept keyword arguments time_stamp
  and data_label which allow the time stamp and dataset label to be set when creating a
  file. (:issue:`6545`)
- ``pandas.io.gbq`` now handles reading unicode strings properly. (:issue:`5940`)

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

- perf improvements in DataFrame construction with certain offsets, by removing faulty caching
  (e.g. MonthEnd,BusinessMonthEnd), (:issue:`6479`)
- Improve performance of ``CustomBusinessDay`` (:issue:`6584`)
- improve performance of slice indexing on Series with string keys (:issue:`6341`, :issue:`6372`)

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

There are no experimental changes in 0.14.0

Bug Fixes
~~~~~~~~~

See :ref:`V0.14.0 Bug Fixes<release.bug_fixes-0.14.0>` for an extensive list of bugs that have been fixed in 0.14.0.

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