API: Accept 'axis' keyword argument for reindex

Author: TomAugspurger

doc/source/basics.rst

@@ -1217,6 +1217,15 @@ following can be done:
 This means that the reindexed Series's index is the same Python object as the
 DataFrame's index.
 
+.. versionadded:: 0.21.0
+
+:meth:`DataFrame.reindex` also supports an "axis-style" calling convention,
+where you specify a single ``labels`` argument and the ``axis`` it applies to.
+
+.. ipython:: python
+
+   df.reindex(['c', 'f', 'b'], axis='index')
+   df.reindex(['three', 'two', 'one'], axis='columns')
 
 .. seealso::
 
@@ -1413,12 +1422,23 @@ Series can also be used:
 
 .. ipython:: python
 
-   df.rename(columns={'one' : 'foo', 'two' : 'bar'},
-             index={'a' : 'apple', 'b' : 'banana', 'd' : 'durian'})
+   df.rename(columns={'one': 'foo', 'two': 'bar'},
+             index={'a': 'apple', 'b': 'banana', 'd': 'durian'})
 
 If the mapping doesn't include a column/index label, it isn't renamed. Also
 extra labels in the mapping don't throw an error.
 
+.. versionadded:: 0.21.0
+
+:meth:`DataFrame.rename` also supports an "axis-style" calling convention, where
+you specify a single ``mapper`` and the ``axis`` to apply that mapping to.
+
+.. ipython:: python
+
+   df.rename({'one': 'foo', 'two': 'bar'}, axis='columns'})
+   df.rename({'a': 'apple', 'b': 'banana', 'd': 'durian'}, axis='columns'})
+
+
 The :meth:`~DataFrame.rename` method also provides an ``inplace`` named
 parameter that is by default ``False`` and copies the underlying data. Pass
 ``inplace=True`` to rename the data in place.

doc/source/whatsnew/v0.21.0.txt

@@ -111,20 +111,39 @@ For example:
     # the following is now equivalent
     df.drop(columns=['B', 'C'])
 
-``rename`` now also accepts axis keyword
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+.. _whatsnew_0210.enhancements.rename_reindex_axis:
 
-The :meth:`~DataFrame.rename` method has gained the ``axis`` keyword as an
-alternative to specify the ``axis`` to target (:issue:`12392`).
+``rename``, ``reindex`` now also accept axis keyword
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-.. ipython:: 
+The :meth:`DataFrame.rename` and :meth:`DataFrame.reindex` methods have gained
+the ``axis`` keyword to specify the axis to target with the operation
+(:issue:`12392`).
+
+Here's ``rename``:
+
+.. ipython:: python
+
+   df = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]})
+   df.rename(str.lower, axis='columns')
+   df.rename(id, axis='index')
+
+And ``reindex``:
+
+.. ipython:: python
+
+   df.reindex(['A', 'B', 'C'], axis='columns')
+   df.reindex([0, 1, 3], axis='index')
+
+The "index, columns" style continues to work as before.
+
+.. ipython:: python
 
-    df = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]})
-    df.rename(str.lower, axis='columns')
-    df.rename(id, axis='index')
+   df.rename(index=id, columns=str.lower)
+   df.reindex(index=[0, 1, 3], columns=['A', 'B', 'C'])
 
-The ``.rename(index=id, columns=str.lower)`` style continues to work as before.
-We *highly* encourage using named arguments to avoid confusion.
+We *highly* encourage using named arguments to avoid confusion when using either
+style.
 
 .. _whatsnew_0210.enhancements.categorical_dtype:
 

pandas/core/frame.py

@@ -65,6 +65,7 @@
                                 _values_from_object,
                                 _maybe_box_datetimelike,
                                 _dict_compat,
+                                _all_not_none,
                                 standardize_mapping)
 from pandas.core.generic import NDFrame, _shared_docs
 from pandas.core.index import (Index, MultiIndex, _ensure_index,
@@ -112,10 +113,10 @@
         by : str or list of str
             Name or list of names which refer to the axis items.""",
     versionadded_to_excel='',
-    optional_mapper="""mapper : dict-like or function
-            Applied to the axis specified by `axis`""",
+    optional_labels="""labels : array-like, optional
+            New labels / index to conform the axis specified by 'axis' to.""",
     optional_axis="""axis : int or str, optional
-            Axis to target. Can be either the axis name ('rows', 'columns')
+            Axis to target. Can be either the axis name ('index', 'columns')
             or number (0, 1).""",
 )
 
@@ -2801,24 +2802,25 @@ def _validate_axis_style_args(self, arg, arg_name, index, columns,
             elif axis == 'columns':
                 columns = arg
 
-        elif all(x is not None for x in (arg, index, columns)):
+        elif _all_not_none(arg, index, columns):
             msg = (
                 "Cannot specify all of '{arg_name}', 'index', and 'columns'. "
                 "Specify either {arg_name} and 'axis', or 'index' and "
                 "'columns'."
             ).format(arg_name=arg_name)
             raise TypeError(msg)
 
-        elif axis is None and (arg is not None and index is not None):
+        elif _all_not_none(arg, index):
             # This is the "ambiguous" case, so emit a warning
             msg = (
                 "Interpreting call to '.{method_name}(a, b)' as "
                 "'.{method_name}(index=a, columns=b)'. "
                 "Use keyword arguments to remove any ambiguity."
             ).format(method_name=method_name)
-            warnings.warn(msg)
+            warnings.warn(msg, stacklevel=3)
             index, columns = arg, index
-        elif index is None and columns is None:
+        elif index is None:
+            # This is for the default axis, like reindex([0, 1])
             index = arg
         return index, columns
 
@@ -2948,7 +2950,11 @@ def align(self, other, join='outer', axis=None, level=None, copy=True,
                                             broadcast_axis=broadcast_axis)
 
     @Appender(_shared_docs['reindex'] % _shared_doc_kwargs)
-    def reindex(self, index=None, columns=None, **kwargs):
+    def reindex(self, labels=None, index=None, columns=None, axis=None,
+                **kwargs):
+        index, columns = self._validate_axis_style_args(labels, 'labels',
+                                                        index, columns,
+                                                        axis, 'reindex')
         return super(DataFrame, self).reindex(index=index, columns=columns,
                                               **kwargs)
 
@@ -2960,9 +2966,81 @@ def reindex_axis(self, labels, axis=0, method=None, level=None, copy=True,
                                         method=method, level=level, copy=copy,
                                         limit=limit, fill_value=fill_value)
 
-    @Appender(_shared_docs['rename'] % _shared_doc_kwargs)
     def rename(self, mapper=None, index=None, columns=None, axis=None,
                **kwargs):
+        """Alter axes labels.
+
+        Function / dict values must be unique (1-to-1). Labels not contained in
+        a dict / Series will be left as-is. Extra labels listed don't throw an
+        error.
+
+        See the :ref:`user guide <basics.rename>` for more.
+
+        Parameters
+        ----------
+        mapper, index, columns : dict-like or function, optional
+            dict-like or functions transformations to apply to
+            that axis' values. Use either ``mapper`` and ``axis`` to
+            specify the axis to target with ``mapper``, or ``index`` and
+            ``columns``.
+        axis : int or str, optional
+            Axis to target with ``mapper``. Can be either the axis name
+            ('index', 'columns') or number (0, 1). The default is 'index'.
+        copy : boolean, default True
+            Also copy underlying data
+        inplace : boolean, default False
+            Whether to return a new %(klass)s. If True then value of copy is
+            ignored.
+        level : int or level name, default None
+            In case of a MultiIndex, only rename labels in the specified
+            level.
+
+        Returns
+        -------
+        renamed : DataFrame
+
+        See Also
+        --------
+        pandas.DataFrame.rename_axis
+
+        Examples
+        --------
+
+        ``DataFrame.rename`` supports two calling conventions
+
+        * ``(index=index_mapper, columns=columns_mapper, ...)
+        * ``(mapper, axis={'index', 'columns'}, ...)
+
+        We *highly* recommend using keyword arguments to clarify your
+        intent.
+
+        >>> df = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]})
+        >>> df.rename(index=str, columns={"A": "a", "B": "c"})
+           a  c
+        0  1  4
+        1  2  5
+        2  3  6
+
+        >>> df.rename(index=str, columns={"A": "a", "C": "c"})
+           a  B
+        0  1  4
+        1  2  5
+        2  3  6
+
+        Using axis-style parameters
+
+        >>> df.rename(str.lower, axis='columns')
+           a  b
+        0  1  4
+        1  2  5
+        2  3  6
+
+        >>> df.rename({1: 2, 2: 4}, axis='index')
+           A  B
+        0  1  4
+        2  2  5
+        4  3  6
+        """
         index, columns = self._validate_axis_style_args(mapper, 'mapper',
                                                         index, columns,
                                                         axis, 'rename')

pandas/core/generic.py

@@ -768,6 +768,7 @@ def swaplevel(self, i=-2, j=-1, axis=0):
 
         Examples
         --------
+
         >>> s = pd.Series([1, 2, 3])
         >>> s
         0    1
@@ -790,16 +791,29 @@ def swaplevel(self, i=-2, j=-1, axis=0):
         5    3
         dtype: int64
 
+        Since ``DataFrame`` doesn't have a ``.name`` attribute,
+        only mapping-type arguments are allowed.
+
         >>> df = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]})
         >>> df.rename(2)
         Traceback (most recent call last):
         ...
         TypeError: 'int' object is not callable
+
+        ``DataFrame.rename`` supports two calling conventions
+
+        * ``(index=index_mapper, columns=columns_mapper, ...)
+        * ``(mapper, axis={'index', 'columns'}, ...)
+
+        We *highly* recommend using keyword arguments to clarify your
+        intent.
+
         >>> df.rename(index=str, columns={"A": "a", "B": "c"})
            a  c
         0  1  4
         1  2  5
         2  3  6
+
         >>> df.rename(index=str, columns={"A": "a", "C": "c"})
            a  B
         0  1  4
@@ -819,6 +833,8 @@ def swaplevel(self, i=-2, j=-1, axis=0):
         0  1  4
         2  2  5
         4  3  6
+
+        See the :ref:`user guide <basics.rename>` for more.
         """
 
     @Appender(_shared_docs['rename'] % dict(axes='axes keywords for this'
@@ -904,6 +920,7 @@ def rename_axis(self, mapper, axis=0, copy=True, inplace=False):
 
         Examples
         --------
+
         >>> df = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]})
         >>> df.rename_axis("foo")  # scalar, alters df.index.name
              A  B
@@ -2764,10 +2781,11 @@ def sort_index(self, axis=0, level=None, ascending=True, inplace=False,
 
         Parameters
         ----------
-        %(axes)s : array-like, optional (can be specified in order, or as
-            keywords)
+        %(optional_labels)s
+        %(axes)s : array-like, optional (should be specified using keywords)
             New labels / index to conform to. Preferably an Index object to
             avoid duplicating data
+        %(optional_axis)s
         method : {None, 'backfill'/'bfill', 'pad'/'ffill', 'nearest'}, optional
             method to use for filling holes in reindexed DataFrame.
             Please note: this is only  applicable to DataFrames/Series with a
@@ -2799,6 +2817,14 @@ def sort_index(self, axis=0, level=None, ascending=True, inplace=False,
         Examples
         --------
 
+        ``DataFrame.reindex`` supports two calling conventions
+
+        * ``(index=index_labels, columns=column_labels, ...)
+        * ``(labels, axis={'index', 'columns'}, ...)
+
+        We *highly* recommend using keyword arguments to clarify your
+        intent.
+
         Create a dataframe with some fictional data.
 
         >>> index = ['Firefox', 'Chrome', 'Safari', 'IE10', 'Konqueror']
@@ -2849,6 +2875,26 @@ def sort_index(self, axis=0, level=None, ascending=True, inplace=False,
         IE10                  404          0.08
         Chrome                200          0.02
 
+        We can also reindex the columns.
+
+        >>> df.reindex(columns=['http_status', 'user_agent'])
+                   http_status  user_agent
+        Firefox            200         NaN
+        Chrome             200         NaN
+        Safari             404         NaN
+        IE10               404         NaN
+        Konqueror          301         NaN
+
+        Or we can use "axis-style" keyword arguments
+
+        >>> df.reindex(['http_status', 'user_agent'], axis="columns")
+                   http_status  user_agent
+        Firefox            200         NaN
+        Chrome             200         NaN
+        Safari             404         NaN
+        IE10               404         NaN
+        Konqueror          301         NaN
+
         To further illustrate the filling functionality in
         ``reindex``, we will create a dataframe with a
         monotonically increasing index (for example, a sequence
@@ -2911,6 +2957,8 @@ def sort_index(self, axis=0, level=None, ascending=True, inplace=False,
         desired indexes. If you do want to fill in the ``NaN`` values present
         in the original dataframe, use the ``fillna()`` method.
 
+        See the :ref:`user guide <basics.reindexing>` for more.
+
         Returns
         -------
         reindexed : %(klass)s
@@ -2919,7 +2967,9 @@ def sort_index(self, axis=0, level=None, ascending=True, inplace=False,
     # TODO: Decide if we care about having different examples for different
     #       kinds
 
-    @Appender(_shared_docs['reindex'] % dict(axes="axes", klass="NDFrame"))
+    @Appender(_shared_docs['reindex'] % dict(axes="axes", klass="NDFrame",
+                                             optional_labels="",
+                                             optional_axis=""))
     def reindex(self, *args, **kwargs):
 
         # construct the args

pandas/core/panel.py

@@ -40,7 +40,7 @@
     axes='items, major_axis, minor_axis',
     klass="Panel",
     axes_single_arg="{0, 1, 2, 'items', 'major_axis', 'minor_axis'}",
-    optional_mapper='', optional_axis='')
+    optional_mapper='', optional_axis='', optional_labels='')
 _shared_doc_kwargs['args_transpose'] = ("three positional arguments: each one"
                                         "of\n%s" %
                                         _shared_doc_kwargs['axes_single_arg'])