DOC: Fix the following 'errors' (pandas-dev#24178):

doc/source/groupby.rst:72:18: F821 undefined name 'obj'
doc/source/groupby.rst:72:30: F821 undefined name 'key'
doc/source/groupby.rst:73:18: F821 undefined name 'obj'
doc/source/groupby.rst:73:30: F821 undefined name 'key'
doc/source/groupby.rst:74:18: F821 undefined name 'obj'
doc/source/groupby.rst:74:31: F821 undefined name 'key1'
doc/source/groupby.rst:74:37: F821 undefined name 'key2'

Author: LJArendse

doc/source/groupby.rst

@@ -62,16 +62,30 @@ See the :ref:`cookbook<cookbook.grouping>` for some advanced strategies.
 Splitting an object into groups
 -------------------------------
 
-pandas objects can be split on any of their axes. The abstract definition of
+Pandas objects can be split on any of their axes. The abstract definition of
 grouping is to provide a mapping of labels to group names. To create a GroupBy
-object (more on what the GroupBy object is later), you may do the following:
+object, see below (more on what the GroupBy object is later). A
+groupby can be applied in the following ways to a pandas object:
+
+* grouped = obj.groupby(key)
+* grouped = obj.groupby(key, axis='columns')
+* grouped = obj.groupby([key1, key2])
 
 .. code-block:: python
 
-   # default is axis=0
-   >>> grouped = obj.groupby(key)
-   >>> grouped = obj.groupby(key, axis=1)
-   >>> grouped = obj.groupby([key1, key2])
+    df = pd.DataFrame(
+        [('bird', 'Falconiformes', 389.0),
+         ('bird', 'Psittaciformes', 24.0),
+         ('mammal', 'Carnivora', 80.2),
+         ('mammal', 'Primates', np.nan),
+         ('mammal', 'Carnivora', 58)],
+        index=['falcon', 'parrot', 'lion', 'monkey', 'leopard'],
+        columns=('class', 'order', 'max_speed')
+    )
+
+    grouped = df.groupby('class')
+    grouped = df.groupby('order', axis='columns')
+    grouped = df.groupby(['class', 'order'])
 
 The mapping can be specified many different ways: