BUG: Allow Series with same name with crosstab (#16028)

Closes gh-13279

Author: mroeschke

doc/source/whatsnew/v0.21.0.txt

@@ -312,6 +312,7 @@ Reshaping
 - Bug when using :func:`isin` on a large object series and large comparison array (:issue:`16012`)
 - Fixes regression from 0.20, :func:`Series.aggregate` and :func:`DataFrame.aggregate` allow dictionaries as return values again (:issue:`16741`)
 - Fixes dtype of result with integer dtype input, from :func:`pivot_table` when called with ``margins=True`` (:issue:`17013`)
+- Bug in ``pd.crosstab()`` where passing two ``Series`` with the same name raised a ``KeyError`` (:issue:`13279`)
 
 Numeric
 ^^^^^^^

pandas/core/reshape/pivot.py

@@ -148,8 +148,17 @@ def pivot_table(data, values=None, index=None, columns=None, aggfunc='mean',
 
     table = agged
     if table.index.nlevels > 1:
-        to_unstack = [agged.index.names[i] or i
-                      for i in range(len(index), len(keys))]
+        # Related GH #17123
+        # If index_names are integers, determine whether the integers refer
+        # to the level position or name.
+        index_names = agged.index.names[:len(index)]
+        to_unstack = []
+        for i in range(len(index), len(keys)):
+            name = agged.index.names[i]
+            if name is None or name in index_names:
+                to_unstack.append(i)
+            else:
+                to_unstack.append(name)
         table = agged.unstack(to_unstack)
 
     if not dropna:

pandas/tests/reshape/test_pivot.py

@@ -1513,6 +1513,16 @@ def test_crosstab_with_numpy_size(self):
                                 columns=expected_column)
         tm.assert_frame_equal(result, expected)
 
+    def test_crosstab_dup_index_names(self):
+        # GH 13279
+        s = pd.Series(range(3), name='foo')
+        result = pd.crosstab(s, s)
+        expected_index = pd.Index(range(3), name='foo')
+        expected = pd.DataFrame(np.eye(3, dtype=np.int64),
+                                index=expected_index,
+                                columns=expected_index)
+        tm.assert_frame_equal(result, expected)
+
 
 class TestPivotAnnual(object):
     """