BUG: Crosstab bug in #18321

doc/source/whatsnew/v0.23.0.txt

@@ -509,6 +509,7 @@ Reshaping
 - Bug in :func:`DataFrame.merge` in which merging using ``Index`` objects as vectors raised an Exception (:issue:`19038`)
 - Bug in :func:`DataFrame.stack`, :func:`DataFrame.unstack`, :func:`Series.unstack` which were not returning subclasses (:issue:`15563`)
 - Bug in timezone comparisons, manifesting as a conversion of the index to UTC in ``.concat()`` (:issue:`18523`)
+- Bug in :func:`crosstab` when performing crosstab operation on two series with tupple name, the resulting data frame has incorrectly named output columns (:issue:`18321`)
 -
 
 Numeric

pandas/core/reshape/pivot.py

@@ -455,17 +455,25 @@ def crosstab(index, columns, values=None, rownames=None, colnames=None,
 
     from pandas import DataFrame
     df = DataFrame(data, index=common_idx)
+    common_cols_idx = df.columns
+
+    # adding dummy column for calculation of pivot table
     if values is None:
         df['__dummy__'] = 0
         kwargs = {'aggfunc': len, 'fill_value': 0}
     else:
         df['__dummy__'] = values
         kwargs = {'aggfunc': aggfunc}
 
-    table = df.pivot_table('__dummy__', index=rownames, columns=colnames,
+    table = df.pivot_table(['__dummy__'], index=rownames, columns=colnames,
                            margins=margins, margins_name=margins_name,
                            dropna=dropna, **kwargs)
 
+    # since column dummy is before computing pivot table, it has to be removed
+    if not table.empty:
+        added_cols_idx = list(df.columns.difference(common_cols_idx))[0]
+        table = table[added_cols_idx]
+
     # Post-process
     if normalize is not False:
         table = _normalize(table, normalize=normalize, margins=margins,

pandas/tests/reshape/test_pivot.py

@@ -1628,7 +1628,8 @@ def test_crosstab_dup_index_names(self):
         pytest.raises(ValueError, pd.crosstab, s, s)
 
     @pytest.mark.parametrize("names", [['a', ('b', 'c')],
-                                       [('a', 'b'), 'c']])
+                                       [('a', 'b'), 'c'],
+                                       [('a', 'b'), ('c', 'd')]])
     def test_crosstab_tuple_name(self, names):
         s1 = pd.Series(range(3), name=names[0])
         s2 = pd.Series(range(1, 4), name=names[1])
@@ -1638,3 +1639,21 @@ def test_crosstab_tuple_name(self, names):
 
         result = pd.crosstab(s1, s2)
         tm.assert_frame_equal(result, expected)
+
+    @pytest.mark.parametrize("names, input_data, expected_data_out", [
+        (['a', 'b'], [[1, 2, 3], [1, 1, 1]], [1, 1, 1]),
+        ([('a', 'b'), 'c'], [[1, 2, 2], [1, 1, 1]], [1, 2]),
+        ([('a', 'b'), ('c', 'd')], [[1, 2, 3], [1, 2, 3]],
+         np.eye(3, dtype=int))])
+    def test_crosstab_cols_output(self, names, input_data, expected_data_out):
+        row_series = pd.Series(input_data[0], name=names[0])
+        col_series = pd.Series(input_data[1], name=names[1])
+        expected_crosstab = pd.DataFrame(
+            expected_data_out,
+            index=pd.Index(set(input_data[0]), name=names[0]),
+            columns=pd.Index(set(input_data[1]), name=names[1])
+        )
+        tm.assert_frame_equal(
+            pd.crosstab(row_series, col_series), expected_crosstab,
+            check_exact=True
+        )