DOC: update NDFrame.squeeze docstring (#20269)

Author: villasv

pandas/core/generic.py

@@ -768,18 +768,108 @@ def pop(self, item):
 
     def squeeze(self, axis=None):
         """
-        Squeeze length 1 dimensions.
+        Squeeze 1 dimensional axis objects into scalars.
+
+        Series or DataFrames with a single element are squeezed to a scalar.
+        DataFrames with a single column or a single row are squeezed to a
+        Series. Otherwise the object is unchanged.
+
+        This method is most useful when you don't know if your
+        object is a Series or DataFrame, but you do know it has just a single
+        column. In that case you can safely call `squeeze` to ensure you have a
+        Series.
 
         Parameters
         ----------
-        axis : None, integer or string axis name, optional
-            The axis to squeeze if 1-sized.
+        axis : axis : {0 or ‘index’, 1 or ‘columns’, None}, default None
+            A specific axis to squeeze. By default, all length-1 axes are
+            squeezed.
 
             .. versionadded:: 0.20.0
 
         Returns
         -------
-        scalar if 1-sized, else original object
+        DataFrame, Series, or scalar
+            The projection after squeezing `axis` or all the axes.
+
+        See Also
+        --------
+        Series.iloc : Integer-location based indexing for selecting scalars
+        DataFrame.iloc : Integer-location based indexing for selecting Series
+        Series.to_frame : Inverse of DataFrame.squeeze for a
+            single-column DataFrame.
+
+        Examples
+        --------
+        >>> primes = pd.Series([2, 3, 5, 7])
+
+        Slicing might produce a Series with a single value:
+
+        >>> even_primes = primes[primes % 2 == 0]
+        >>> even_primes
+        0    2
+        dtype: int64
+
+        >>> even_primes.squeeze()
+        2
+
+        Squeezing objects with more than one value in every axis does nothing:
+
+        >>> odd_primes = primes[primes % 2 == 1]
+        >>> odd_primes
+        1    3
+        2    5
+        3    7
+        dtype: int64
+
+        >>> odd_primes.squeeze()
+        1    3
+        2    5
+        3    7
+        dtype: int64
+
+        Squeezing is even more effective when used with DataFrames.
+
+        >>> df = pd.DataFrame([[1, 2], [3, 4]], columns=['a', 'b'])
+        >>> df
+           a  b
+        0  1  2
+        1  3  4
+
+        Slicing a single column will produce a DataFrame with the columns
+        having only one value:
+
+        >>> df_a = df[['a']]
+        >>> df_a
+           a
+        0  1
+        1  3
+
+        So the columns can be squeezed down, resulting in a Series:
+
+        >>> df_a.squeeze('columns')
+        0    1
+        1    3
+        Name: a, dtype: int64
+
+        Slicing a single row from a single column will produce a single
+        scalar DataFrame:
+
+        >>> df_0a = df.loc[df.index < 1, ['a']]
+        >>> df_0a
+           a
+        0  1
+
+        Squeezing the rows produces a single scalar Series:
+
+        >>> df_0a.squeeze('rows')
+        a    1
+        Name: 0, dtype: int64
+
+        Squeezing all axes wil project directly into a scalar:
+
+        >>> df_0a.squeeze()
+        1
         """
         axis = (self._AXIS_NAMES if axis is None else
                 (self._get_axis_number(axis),))