Example with and without categories with no data

Now shows correct output for crosstab(foo, bar) and show another example where categories are preserved by setting "dropna=False".

Author: testvinder

pandas/core/reshape/pivot.py

@@ -429,9 +429,19 @@ def crosstab(index, columns, values=None, rownames=None, colnames=None,
 
     >>> foo = pd.Categorical(['a', 'b'], categories=['a', 'b', 'c'])
     >>> bar = pd.Categorical(['d', 'e'], categories=['d', 'e', 'f'])
+    >>> crosstab(foo, bar)  # 'c' and 'f' are not represented in the data, 
+                            # and will not be shown in the output because
+                            # dropna is True by default. Set 'dropna=False'
+                            # to preserve categories with no data
+    ... # doctest: +SKIP
+    col_0  d  e
+    row_0
+    a      1  0
+    b      0  1
+
     >>> crosstab(foo, bar, dropna=False)  # 'c' and 'f' are not represented
-                            # in the data, but they still will be counted in
-                            # the output
+                            # in the data, but they still will be counted 
+                            # and shown in the output
     ... # doctest: +SKIP
     col_0  d  e  f
     row_0