From a748ccd24071e268998d5f26348b54485e3fdd7d Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Fri, 7 Jun 2019 16:39:53 -0400
Subject: [PATCH 01/36] BUG: Check for duplicate names in columns and index
 when calling crosstab

---
 pandas/core/reshape/pivot.py | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index d653dd87308cf..47cacedb57e06 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -543,6 +543,17 @@ def crosstab(
 
     common_idx = _get_objs_combined_axis(index + columns, intersect=True, sort=False)
 
+    if len(set(rownames)) != len(rownames):
+        raise ValueError("Duplicated index/row names not allowed")
+    if len(set(colnames)) != len(colnames):
+        raise ValueError("Duplicated column names not allowed")
+
+    repeated_names = set(rownames).intersection(set(colnames))
+    if repeated_names:
+        raise ValueError("Column and rows cannot share the same names. "
+                         "Repeated names: {repeated_names}"
+                         .format(repeated_names=", ".join(repeated_names)))
+
     data = {}
     data.update(zip(rownames, index))
     data.update(zip(colnames, columns))

From c5430abe1d7cb6eb93aca57b866dabfa4302c0b1 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sun, 9 Jun 2019 12:41:47 -0400
Subject: [PATCH 02/36] Updated test for duplicated names in crosstab

---
 pandas/tests/reshape/test_pivot.py | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/pandas/tests/reshape/test_pivot.py b/pandas/tests/reshape/test_pivot.py
index 582084e3bfb5a..ee7a5dcd52f73 100644
--- a/pandas/tests/reshape/test_pivot.py
+++ b/pandas/tests/reshape/test_pivot.py
@@ -2440,16 +2440,29 @@ def test_crosstab_with_numpy_size(self):
         )
         tm.assert_frame_equal(result, expected)
 
+
     def test_crosstab_dup_index_names(self):
-        # GH 13279
-        s = pd.Series(range(3), name="foo")
+        s1 = pd.Series(range(3), name='foo')
+        s2 = s1 + 1
+
+        msg = "Column and rows cannot share the same names. Repeated names: foo"
+        with pytest.raises(ValueError, match=msg):
+            pd.crosstab(s1, s2)
+        with pytest.raises(ValueError, match=msg):
+            pd.crosstab(s1, [s2, s2.rename("bar")])
+
+        msg = "Duplicated column names not allowed"
+        with pytest.raises(ValueError, match=msg):
+            pd.crosstab(s1.rename("bar"), [s2, s2])
+        with pytest.raises(ValueError, match=msg):
+            pd.crosstab(s1.rename("bar"), [s2.rename("one"), s2, s2])
+
+        msg = "Duplicated index/row names not allowed"
+        with pytest.raises(ValueError, match=msg):
+            pd.crosstab([s1, s1], s2.rename("bar"))
+        with pytest.raises(ValueError, match=msg):
+            pd.crosstab([s1, s1, s1.rename("one")], s2.rename("bar"))
 
-        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)
 
     @pytest.mark.parametrize("names", [["a", ("b", "c")], [("a", "b"), "c"]])
     def test_crosstab_tuple_name(self, names):

From 5762bb68bffcdfdd1aabee9d309a52b2e1a05992 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sun, 9 Jun 2019 12:46:22 -0400
Subject: [PATCH 03/36] Flake8 compliance

---
 pandas/tests/reshape/test_pivot.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pandas/tests/reshape/test_pivot.py b/pandas/tests/reshape/test_pivot.py
index ee7a5dcd52f73..aada1cf0d4062 100644
--- a/pandas/tests/reshape/test_pivot.py
+++ b/pandas/tests/reshape/test_pivot.py
@@ -2445,7 +2445,8 @@ def test_crosstab_dup_index_names(self):
         s1 = pd.Series(range(3), name='foo')
         s2 = s1 + 1
 
-        msg = "Column and rows cannot share the same names. Repeated names: foo"
+        msg = "Column and rows cannot share the same names. " \
+              "Repeated names: foo"
         with pytest.raises(ValueError, match=msg):
             pd.crosstab(s1, s2)
         with pytest.raises(ValueError, match=msg):

From 989bd5aba7f9bae541694a215cc6d2f032940647 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Mon, 16 Sep 2019 21:19:03 -0400
Subject: [PATCH 04/36] Black formatting

---
 pandas/core/reshape/pivot.py       | 9 ++++++---
 pandas/tests/reshape/test_pivot.py | 9 ++++-----
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 47cacedb57e06..38aa78dcd11c2 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -550,9 +550,12 @@ def crosstab(
 
     repeated_names = set(rownames).intersection(set(colnames))
     if repeated_names:
-        raise ValueError("Column and rows cannot share the same names. "
-                         "Repeated names: {repeated_names}"
-                         .format(repeated_names=", ".join(repeated_names)))
+        raise ValueError(
+            "Column and rows cannot share the same names. "
+            "Repeated names: {repeated_names}".format(
+                repeated_names=", ".join(repeated_names)
+            )
+        )
 
     data = {}
     data.update(zip(rownames, index))
diff --git a/pandas/tests/reshape/test_pivot.py b/pandas/tests/reshape/test_pivot.py
index aada1cf0d4062..c859d57fd89a8 100644
--- a/pandas/tests/reshape/test_pivot.py
+++ b/pandas/tests/reshape/test_pivot.py
@@ -2440,13 +2440,13 @@ def test_crosstab_with_numpy_size(self):
         )
         tm.assert_frame_equal(result, expected)
 
-
     def test_crosstab_dup_index_names(self):
-        s1 = pd.Series(range(3), name='foo')
+        # Duplicate names/index/rows in crosstab are not supported
+
+        s1 = pd.Series(range(3), name="foo")
         s2 = s1 + 1
 
-        msg = "Column and rows cannot share the same names. " \
-              "Repeated names: foo"
+        msg = "Column and rows cannot share the same names. Repeated names: foo"
         with pytest.raises(ValueError, match=msg):
             pd.crosstab(s1, s2)
         with pytest.raises(ValueError, match=msg):
@@ -2464,7 +2464,6 @@ def test_crosstab_dup_index_names(self):
         with pytest.raises(ValueError, match=msg):
             pd.crosstab([s1, s1, s1.rename("one")], s2.rename("bar"))
 
-
     @pytest.mark.parametrize("names", [["a", ("b", "c")], [("a", "b"), "c"]])
     def test_crosstab_tuple_name(self, names):
         s1 = pd.Series(range(3), name=names[0])

From 672bd4b5d1a6bdd0780e9438728c1c72faea462f Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Thu, 19 Sep 2019 23:28:37 -0400
Subject: [PATCH 05/36] Creates name mapping to overcome duplicated columns
 issues in pd.crosstab()

---
 pandas/core/reshape/pivot.py       | 96 +++++++++++++++++++++---------
 pandas/tests/reshape/test_pivot.py | 53 ++++++++++++-----
 2 files changed, 106 insertions(+), 43 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 38aa78dcd11c2..bfa46fb24d265 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -534,42 +534,38 @@ def crosstab(
     b      0  1  0
     c      0  0  0
     """
+    if values is None and aggfunc is not None:
+        raise ValueError("aggfunc cannot be used without values.")
+
+    if values is not None and aggfunc is None:
+        raise ValueError("values cannot be used without an aggfunc.")
 
     index = com.maybe_make_list(index)
     columns = com.maybe_make_list(columns)
 
+    common_idx = _get_objs_combined_axis(index + columns, intersect=True, sort=False)
+
     rownames = _get_names(index, rownames, prefix="row")
     colnames = _get_names(columns, colnames, prefix="col")
 
-    common_idx = _get_objs_combined_axis(index + columns, intersect=True, sort=False)
+    # We create our own mapping of row and columns names
+    # to prevent issues with duplicate columns. GH Issue: #22529
+    shared_col_row_names = set(rownames).intersection(set(colnames))
+    row_names_mapper, unique_row_names = _build_names_mapper(
+        rownames, shared_col_row_names, "row"
+    )
+    col_names_mapper, unique_col_names = _build_names_mapper(
+        colnames, shared_col_row_names, "col"
+    )
 
-    if len(set(rownames)) != len(rownames):
-        raise ValueError("Duplicated index/row names not allowed")
-    if len(set(colnames)) != len(colnames):
-        raise ValueError("Duplicated column names not allowed")
-
-    repeated_names = set(rownames).intersection(set(colnames))
-    if repeated_names:
-        raise ValueError(
-            "Column and rows cannot share the same names. "
-            "Repeated names: {repeated_names}".format(
-                repeated_names=", ".join(repeated_names)
-            )
-        )
+    from pandas import DataFrame
 
     data = {}
-    data.update(zip(rownames, index))
-    data.update(zip(colnames, columns))
-
-    if values is None and aggfunc is not None:
-        raise ValueError("aggfunc cannot be used without values.")
-
-    if values is not None and aggfunc is None:
-        raise ValueError("values cannot be used without an aggfunc.")
-
-    from pandas import DataFrame
+    data.update(zip(unique_row_names, index))
+    data.update(zip(unique_col_names, columns))
 
     df = DataFrame(data, index=common_idx)
+
     if values is None:
         df["__dummy__"] = 0
         kwargs = {"aggfunc": len, "fill_value": 0}
@@ -579,12 +575,12 @@ def crosstab(
 
     table = df.pivot_table(
         "__dummy__",
-        index=rownames,
-        columns=colnames,
+        index=unique_row_names,
+        columns=unique_col_names,
         margins=margins,
         margins_name=margins_name,
         dropna=dropna,
-        **kwargs
+        **kwargs,
     )
 
     # Post-process
@@ -593,6 +589,11 @@ def crosstab(
             table, normalize=normalize, margins=margins, margins_name=margins_name
         )
 
+    print(row_names_mapper)
+    print(col_names_mapper)
+    table = table.rename_axis(index=row_names_mapper, axis=0)
+    table = table.rename_axis(columns=col_names_mapper, axis=1)
+
     return table
 
 
@@ -692,3 +693,44 @@ def _get_names(arrs, names, prefix="row"):
             names = list(names)
 
     return names
+
+
+def _get_duplicate_count(names_list):
+    seen_names = set()
+    duplicate_names = {}
+    for name in names_list:
+        if name not in seen_names:
+            duplicate_names[name] = 0
+            seen_names.add(name)
+        else:
+            duplicate_names[name] += 1
+
+    return duplicate_names
+
+
+def _build_names_mapper(names, shared_col_row_names, suffix):
+
+    dup_names_count = _get_duplicate_count(names)
+    names_mapper = {}
+    unique_names = []
+
+    # We reserve the names so the number are in order of appearance
+    for name in reversed(names):
+        mapped_name = name
+        num_duplicates = dup_names_count[name]
+
+        # Add a number if it is duplicated
+        if num_duplicates > 0:
+            mapped_name = f"{mapped_name}_{num_duplicates}"
+            dup_names_count[name] -= 1
+
+        # Add suffix if it is shared between column and rows
+        if name in shared_col_row_names:
+            mapped_name = f"{mapped_name}_{suffix}"
+
+        names_mapper[mapped_name] = name
+
+        # Creates a list of names in the original order
+        unique_names.insert(0, mapped_name)
+
+    return names_mapper, unique_names
diff --git a/pandas/tests/reshape/test_pivot.py b/pandas/tests/reshape/test_pivot.py
index c859d57fd89a8..042f58aef05e1 100644
--- a/pandas/tests/reshape/test_pivot.py
+++ b/pandas/tests/reshape/test_pivot.py
@@ -2441,28 +2441,49 @@ def test_crosstab_with_numpy_size(self):
         tm.assert_frame_equal(result, expected)
 
     def test_crosstab_dup_index_names(self):
-        # Duplicate names/index/rows in crosstab are not supported
+        # We test that duplicated column names do not produce issues
+        # GH Issue: #22529
 
+        # Duplicate name shared between rows and columns
         s1 = pd.Series(range(3), name="foo")
         s2 = s1 + 1
+        expected = pd.crosstab(s1, s2.rename("bar"))
+        result = pd.crosstab(s1, s2)
+        tm.assert_frame_equal(
+            result, expected.rename_axis(columns={"bar": "foo"}, axis=1)
+        )
+        assert result.index.names == ["foo"]
+        assert result.columns.names == ["foo"]
 
-        msg = "Column and rows cannot share the same names. Repeated names: foo"
-        with pytest.raises(ValueError, match=msg):
-            pd.crosstab(s1, s2)
-        with pytest.raises(ValueError, match=msg):
-            pd.crosstab(s1, [s2, s2.rename("bar")])
+        # Row names duplicated
+        s1 = pd.Series(range(3), name="foo")
+        s2 = s1 + 1
+        s3 = pd.Series(range(3), name="bar_col")
 
-        msg = "Duplicated column names not allowed"
-        with pytest.raises(ValueError, match=msg):
-            pd.crosstab(s1.rename("bar"), [s2, s2])
-        with pytest.raises(ValueError, match=msg):
-            pd.crosstab(s1.rename("bar"), [s2.rename("one"), s2, s2])
+        expected = pd.crosstab([s1, s2.rename("bar")], s3)
+        result = pd.crosstab([s1, s2], s3)
 
-        msg = "Duplicated index/row names not allowed"
-        with pytest.raises(ValueError, match=msg):
-            pd.crosstab([s1, s1], s2.rename("bar"))
-        with pytest.raises(ValueError, match=msg):
-            pd.crosstab([s1, s1, s1.rename("one")], s2.rename("bar"))
+        tm.assert_frame_equal(
+            result, expected.rename_axis(index={"bar": "foo"}, axis=0)
+        )
+
+        assert result.index.names == ["foo", "foo"]
+        assert result.columns.names == ["bar_col"]
+
+        # Column names duplicated
+        s1 = pd.Series(range(3), name="foo")
+        s2 = s1 + 1
+        s3 = pd.Series(range(3), name="bar_row")
+
+        expected = pd.crosstab(s3, [s1, s2.rename("bar")])
+        result = pd.crosstab(s3, [s1, s2])
+
+        tm.assert_frame_equal(
+            result, expected.rename_axis(columns={"bar": "foo"}, axis=1)
+        )
+
+        assert result.index.names == ["bar_row"]
+        assert result.columns.names == ["foo", "foo"]
 
     @pytest.mark.parametrize("names", [["a", ("b", "c")], [("a", "b"), "c"]])
     def test_crosstab_tuple_name(self, names):

From 1b67514ed3f502ea874dca4e5bab45765b4fa3da Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Thu, 19 Sep 2019 23:29:49 -0400
Subject: [PATCH 06/36] Removed debug prints

---
 pandas/core/reshape/pivot.py | 2 --
 1 file changed, 2 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index bfa46fb24d265..5e25343b65419 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -589,8 +589,6 @@ def crosstab(
             table, normalize=normalize, margins=margins, margins_name=margins_name
         )
 
-    print(row_names_mapper)
-    print(col_names_mapper)
     table = table.rename_axis(index=row_names_mapper, axis=0)
     table = table.rename_axis(columns=col_names_mapper, axis=1)
 

From 4f2fa86100252e70f0e81f0fafe3c192e0af5f99 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Thu, 19 Sep 2019 23:30:14 -0400
Subject: [PATCH 07/36] Removed empty line

---
 pandas/core/reshape/pivot.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 5e25343b65419..0728bc76ec5b4 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -707,7 +707,6 @@ def _get_duplicate_count(names_list):
 
 
 def _build_names_mapper(names, shared_col_row_names, suffix):
-
     dup_names_count = _get_duplicate_count(names)
     names_mapper = {}
     unique_names = []

From fbff182b5dbc1edbfd40fba63595f70026f658cf Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Thu, 19 Sep 2019 23:31:20 -0400
Subject: [PATCH 08/36] Improved comments

---
 pandas/core/reshape/pivot.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 0728bc76ec5b4..bcf2be9c9b390 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -711,17 +711,17 @@ def _build_names_mapper(names, shared_col_row_names, suffix):
     names_mapper = {}
     unique_names = []
 
-    # We reserve the names so the number are in order of appearance
+    # We reverse the names so the number are in order of appearance
     for name in reversed(names):
         mapped_name = name
         num_duplicates = dup_names_count[name]
 
-        # Add a number if it is duplicated
+        # Adds a number if name is duplicated within columns/rows
         if num_duplicates > 0:
             mapped_name = f"{mapped_name}_{num_duplicates}"
             dup_names_count[name] -= 1
 
-        # Add suffix if it is shared between column and rows
+        # Add suffix name is shared between column and rows
         if name in shared_col_row_names:
             mapped_name = f"{mapped_name}_{suffix}"
 

From 6071db52a3432e183b97bc18878066b9ec0775ba Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Fri, 20 Sep 2019 00:06:05 -0400
Subject: [PATCH 09/36] String manipulation compatible with <3.6

---
 pandas/core/reshape/pivot.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index bcf2be9c9b390..32c5c427eb334 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -718,12 +718,16 @@ def _build_names_mapper(names, shared_col_row_names, suffix):
 
         # Adds a number if name is duplicated within columns/rows
         if num_duplicates > 0:
-            mapped_name = f"{mapped_name}_{num_duplicates}"
+            mapped_name = "{mapped_name}_{num_duplicates}".format(
+                mapped_name=mapped_name, num_duplicates=num_duplicates
+            )
             dup_names_count[name] -= 1
 
         # Add suffix name is shared between column and rows
         if name in shared_col_row_names:
-            mapped_name = f"{mapped_name}_{suffix}"
+            mapped_name = "{mapped_name}_{suffix}".format(
+                mapped_name=mapped_name, suffix=suffix
+            )
 
         names_mapper[mapped_name] = name
 

From 3d9c632238ef3a3467553e7be830069094628939 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sun, 22 Sep 2019 13:19:38 -0400
Subject: [PATCH 10/36] Replaced custom method with _value_counts_arraylike

---
 pandas/core/reshape/pivot.py | 33 +++++++++++----------------------
 1 file changed, 11 insertions(+), 22 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 32c5c427eb334..2646d76aa322d 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -13,6 +13,7 @@
 from pandas.core.reshape.concat import concat
 from pandas.core.reshape.util import cartesian_product
 from pandas.core.series import Series
+from pandas.core.algorithms import _value_counts_arraylike
 
 
 # Note: We need to make sure `frame` is imported before `pivot`, otherwise
@@ -693,35 +694,23 @@ def _get_names(arrs, names, prefix="row"):
     return names
 
 
-def _get_duplicate_count(names_list):
-    seen_names = set()
-    duplicate_names = {}
-    for name in names_list:
-        if name not in seen_names:
-            duplicate_names[name] = 0
-            seen_names.add(name)
-        else:
-            duplicate_names[name] += 1
-
-    return duplicate_names
-
-
 def _build_names_mapper(names, shared_col_row_names, suffix):
-    dup_names_count = _get_duplicate_count(names)
+    keys, counts = _value_counts_arraylike(names, dropna=False)
+    names_count = dict(zip(keys, counts))
+
     names_mapper = {}
     unique_names = []
-
-    # We reverse the names so the number are in order of appearance
+    # We reverse the names so the numbers are in the order given by the user
     for name in reversed(names):
         mapped_name = name
-        num_duplicates = dup_names_count[name]
+        name_count = names_count[name]
 
         # Adds a number if name is duplicated within columns/rows
-        if num_duplicates > 0:
-            mapped_name = "{mapped_name}_{num_duplicates}".format(
-                mapped_name=mapped_name, num_duplicates=num_duplicates
+        if name_count > 1:
+            mapped_name = "{mapped_name}_{name_count}".format(
+                mapped_name=mapped_name, name_count=name_count
             )
-            dup_names_count[name] -= 1
+            names_count[name] -= 1
 
         # Add suffix name is shared between column and rows
         if name in shared_col_row_names:
@@ -731,7 +720,7 @@ def _build_names_mapper(names, shared_col_row_names, suffix):
 
         names_mapper[mapped_name] = name
 
-        # Creates a list of names in the original order
+        # Creates a list of the new names in the original order
         unique_names.insert(0, mapped_name)
 
     return names_mapper, unique_names

From d27233f5e8ea46b05e7a0373b5f982cba64cbc8e Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Tue, 24 Sep 2019 17:30:31 -0400
Subject: [PATCH 11/36] Resort imports

---
 pandas/core/reshape/pivot.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 2646d76aa322d..dfc1ab771c06a 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -6,6 +6,7 @@
 from pandas.core.dtypes.common import is_integer_dtype, is_list_like, is_scalar
 from pandas.core.dtypes.generic import ABCDataFrame, ABCSeries
 
+from pandas.core.algorithms import _value_counts_arraylike
 import pandas.core.common as com
 from pandas.core.frame import _shared_docs
 from pandas.core.groupby import Grouper
@@ -13,7 +14,6 @@
 from pandas.core.reshape.concat import concat
 from pandas.core.reshape.util import cartesian_product
 from pandas.core.series import Series
-from pandas.core.algorithms import _value_counts_arraylike
 
 
 # Note: We need to make sure `frame` is imported before `pivot`, otherwise

From 3e9333deb94a3ab1a94c868808497c4d24372f05 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Mon, 18 Nov 2019 23:57:14 -0500
Subject: [PATCH 12/36] Added docstring and type hints to _build_names_mapper

---
 pandas/core/reshape/pivot.py       | 26 +++++++++++++++++++++++++-
 pandas/tests/reshape/test_pivot.py |  2 +-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 2399fec928be0..6a8e641d08373 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -1,3 +1,5 @@
+from typing import List, Set, Dict, Tuple
+
 import numpy as np
 
 from pandas.util._decorators import Appender, Substitution
@@ -699,7 +701,29 @@ def _get_names(arrs, names, prefix="row"):
     return names
 
 
-def _build_names_mapper(names, shared_col_row_names, suffix):
+def _build_names_mapper(
+    names: List[str], shared_col_row_names: Set[str], suffix: str
+) -> Tuple[Dict[str, str], List[str]]:
+    """
+    Given a list of row or column names, creates a mapper of unique names to
+    column/row names.
+
+    Parameters
+    ----------
+    names : list
+        Names to be deduplicated.
+    shared_col_row_names : set or list
+        Values used both in rows and columns, so need additional deduplication.
+    suffix : str
+        Suffix to deduplicate values in shared_col_row_names
+
+    Returns
+    -------
+    names_mapper: dict
+        The keys are the unique names and the values are the original names.
+    unique_names: list
+        Unique names in the same order that names came in
+    """
     keys, counts = _value_counts_arraylike(names, dropna=False)
     names_count = dict(zip(keys, counts))
 
diff --git a/pandas/tests/reshape/test_pivot.py b/pandas/tests/reshape/test_pivot.py
index ef86d398750ae..4c4f763ba79d7 100644
--- a/pandas/tests/reshape/test_pivot.py
+++ b/pandas/tests/reshape/test_pivot.py
@@ -2487,7 +2487,7 @@ def test_crosstab_with_numpy_size(self):
 
     def test_crosstab_dup_index_names(self):
         # We test that duplicated column names do not produce issues
-        # GH Issue: #22529
+        # GH Issue: #22529, GH#13279
 
         # Duplicate name shared between rows and columns
         s1 = pd.Series(range(3), name="foo")

From fe6f7fd131673ec598a8d319a32eaebf9cb824dc Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Tue, 19 Nov 2019 09:07:37 -0500
Subject: [PATCH 13/36] Sorted imports

---
 pandas/core/reshape/pivot.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 6a8e641d08373..a969360223bfc 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -1,4 +1,4 @@
-from typing import List, Set, Dict, Tuple
+from typing import Dict, List, Set, Tuple
 
 import numpy as np
 

From 9f4a00ac4a5f530d432eae98c6b6eee3957d4bf6 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Tue, 19 Nov 2019 09:38:22 -0500
Subject: [PATCH 14/36] Added types to unique_names

---
 pandas/core/reshape/pivot.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index a969360223bfc..12fef6c5d3d07 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -728,7 +728,7 @@ def _build_names_mapper(
     names_count = dict(zip(keys, counts))
 
     names_mapper = {}
-    unique_names = []
+    unique_names: List[str] = []
     # We reverse the names so the numbers are in the order given by the user
     for name in reversed(names):
         mapped_name = name

From 788ac2b7c33479d421f4448da7aaae9559e21782 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Wed, 20 Nov 2019 21:39:47 -0500
Subject: [PATCH 15/36] Updated tests

---
 pandas/core/reshape/pivot.py       | 10 +++++-----
 pandas/tests/reshape/test_pivot.py | 24 ++++++++++++------------
 2 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 12fef6c5d3d07..af17afd8ed9c4 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -555,7 +555,7 @@ def crosstab(
     colnames = _get_names(columns, colnames, prefix="col")
 
     # We create our own mapping of row and columns names
-    # to prevent issues with duplicate columns. GH Issue: #22529
+    # to prevent issues with duplicate columns/row names. GH Issue: #22529
     shared_col_row_names = set(rownames).intersection(set(colnames))
     row_names_mapper, unique_row_names = _build_names_mapper(
         rownames, shared_col_row_names, "row"
@@ -566,10 +566,10 @@ def crosstab(
 
     from pandas import DataFrame
 
-    data = {}
-    data.update(zip(unique_row_names, index))
-    data.update(zip(unique_col_names, columns))
-
+    data = {
+        **dict(zip(unique_row_names, index)),
+        **dict(zip(unique_col_names, columns)),
+    }
     df = DataFrame(data, index=common_idx)
 
     if values is None:
diff --git a/pandas/tests/reshape/test_pivot.py b/pandas/tests/reshape/test_pivot.py
index 4c4f763ba79d7..dea52ec7a79bf 100644
--- a/pandas/tests/reshape/test_pivot.py
+++ b/pandas/tests/reshape/test_pivot.py
@@ -2492,11 +2492,11 @@ def test_crosstab_dup_index_names(self):
         # Duplicate name shared between rows and columns
         s1 = pd.Series(range(3), name="foo")
         s2 = s1 + 1
-        expected = pd.crosstab(s1, s2.rename("bar"))
-        result = pd.crosstab(s1, s2)
-        tm.assert_frame_equal(
-            result, expected.rename_axis(columns={"bar": "foo"}, axis=1)
+        expected = pd.crosstab(s1, s2.rename("bar")).rename_axis(
+            columns={"bar": "foo"}, axis=1
         )
+        result = pd.crosstab(s1, s2)
+        tm.assert_frame_equal(result, expected)
         assert result.index.names == ["foo"]
         assert result.columns.names == ["foo"]
 
@@ -2505,12 +2505,12 @@ def test_crosstab_dup_index_names(self):
         s2 = s1 + 1
         s3 = pd.Series(range(3), name="bar_col")
 
-        expected = pd.crosstab([s1, s2.rename("bar")], s3)
+        expected = pd.crosstab([s1, s2.rename("bar")], s3).rename_axis(
+            index={"bar": "foo"}, axis=0
+        )
         result = pd.crosstab([s1, s2], s3)
 
-        tm.assert_frame_equal(
-            result, expected.rename_axis(index={"bar": "foo"}, axis=0)
-        )
+        tm.assert_frame_equal(result, expected)
 
         assert result.index.names == ["foo", "foo"]
         assert result.columns.names == ["bar_col"]
@@ -2520,12 +2520,12 @@ def test_crosstab_dup_index_names(self):
         s2 = s1 + 1
         s3 = pd.Series(range(3), name="bar_row")
 
-        expected = pd.crosstab(s3, [s1, s2.rename("bar")])
+        expected = pd.crosstab(s3, [s1, s2.rename("bar")]).rename_axis(
+            columns={"bar": "foo"}, axis=1
+        )
         result = pd.crosstab(s3, [s1, s2])
 
-        tm.assert_frame_equal(
-            result, expected.rename_axis(columns={"bar": "foo"}, axis=1)
-        )
+        tm.assert_frame_equal(result, expected)
 
         assert result.index.names == ["bar_row"]
         assert result.columns.names == ["foo", "foo"]

From d938a96e264efaeb24fe45dcd0ce59e7f7c935a2 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Thu, 21 Nov 2019 09:14:29 -0500
Subject: [PATCH 16/36] Sorted imports

---
 pandas/core/reshape/pivot.py | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index d74878721cf3e..1b4f4629d02bd 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -1,21 +1,18 @@
-from typing import TYPE_CHECKING, Callable, Dict, List, Tuple, Set, Union
+from typing import TYPE_CHECKING, Callable, Dict, List, Set, Tuple, Union
 
 import numpy as np
-
-from pandas.util._decorators import Appender, Substitution
-
+import pandas.core.common as com
+from pandas.core.algorithms import _value_counts_arraylike
 from pandas.core.dtypes.cast import maybe_downcast_to_dtype
 from pandas.core.dtypes.common import is_integer_dtype, is_list_like, is_scalar
 from pandas.core.dtypes.generic import ABCDataFrame, ABCSeries
-
-from pandas.core.algorithms import _value_counts_arraylike
-import pandas.core.common as com
 from pandas.core.frame import _shared_docs
 from pandas.core.groupby import Grouper
 from pandas.core.index import Index, MultiIndex, get_objs_combined_axis
 from pandas.core.reshape.concat import concat
 from pandas.core.reshape.util import cartesian_product
 from pandas.core.series import Series
+from pandas.util._decorators import Appender, Substitution
 
 if TYPE_CHECKING:
     from pandas import DataFrame

From d60308c12ac7cef4aa789aa5b98bd0b8a9f6121f Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Thu, 21 Nov 2019 17:10:32 -0500
Subject: [PATCH 17/36] Sorted imports

---
 pandas/core/reshape/pivot.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 1b4f4629d02bd..3239ff3794c5e 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -1,18 +1,21 @@
 from typing import TYPE_CHECKING, Callable, Dict, List, Set, Tuple, Union
 
 import numpy as np
-import pandas.core.common as com
-from pandas.core.algorithms import _value_counts_arraylike
+
+from pandas.util._decorators import Appender, Substitution
+
 from pandas.core.dtypes.cast import maybe_downcast_to_dtype
 from pandas.core.dtypes.common import is_integer_dtype, is_list_like, is_scalar
 from pandas.core.dtypes.generic import ABCDataFrame, ABCSeries
+
+from pandas.core.algorithms import _value_counts_arraylike
+import pandas.core.common as com
 from pandas.core.frame import _shared_docs
 from pandas.core.groupby import Grouper
 from pandas.core.index import Index, MultiIndex, get_objs_combined_axis
 from pandas.core.reshape.concat import concat
 from pandas.core.reshape.util import cartesian_product
 from pandas.core.series import Series
-from pandas.util._decorators import Appender, Substitution
 
 if TYPE_CHECKING:
     from pandas import DataFrame

From cad2dea26166bc76da089e32221a9f276a2c02e5 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sat, 11 Apr 2020 11:33:12 -0400
Subject: [PATCH 18/36] Improved comment

---
 pandas/core/reshape/pivot.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 997c140243f2d..f162bade41eca 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -777,7 +777,7 @@ def _build_names_mapper(
             )
             names_count[name] -= 1
 
-        # Add suffix name is shared between column and rows
+        # Add suffix name if column is shared between column and rows
         if name in shared_col_row_names:
             mapped_name = "{mapped_name}_{suffix}".format(
                 mapped_name=mapped_name, suffix=suffix

From f0261e97d01b5a3ed44616bf251f23bd18abfff7 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sat, 11 Apr 2020 13:45:00 -0400
Subject: [PATCH 19/36] Updated tests

---
 pandas/tests/reshape/test_crosstab.py | 46 +++++++++++++++++++++++----
 1 file changed, 40 insertions(+), 6 deletions(-)

diff --git a/pandas/tests/reshape/test_crosstab.py b/pandas/tests/reshape/test_crosstab.py
index 8795af2e11122..6244051ad5f9e 100644
--- a/pandas/tests/reshape/test_crosstab.py
+++ b/pandas/tests/reshape/test_crosstab.py
@@ -534,15 +534,49 @@ def test_crosstab_with_numpy_size(self):
         tm.assert_frame_equal(result, expected)
 
     def test_crosstab_dup_index_names(self):
-        # GH 13279
-        s = Series(range(3), name="foo")
+        # We test that duplicated column names do not produce issues
+        # GH Issue: #22529, GH#13279
 
-        result = crosstab(s, s)
-        expected_index = Index(range(3), name="foo")
-        expected = DataFrame(
-            np.eye(3, dtype=np.int64), index=expected_index, columns=expected_index
+        # Duplicate name shared between rows and columns
+        s1 = pd.Series(range(3), name="foo")
+        s2 = s1 + 1
+        expected = pd.crosstab(s1, s2.rename("bar")).rename_axis(
+            columns={"bar": "foo"}, axis=1
         )
+        result = pd.crosstab(s1, s2)
         tm.assert_frame_equal(result, expected)
+        assert result.index.names == ["foo"]
+        assert result.columns.names == ["foo"]
+
+        # Row names duplicated
+        s1 = pd.Series(range(3), name="foo")
+        s2 = s1 + 1
+        s3 = pd.Series(range(3), name="bar_col")
+
+        expected = pd.crosstab([s1, s2.rename("bar")], s3).rename_axis(
+            index={"bar": "foo"}, axis=0
+        )
+        result = pd.crosstab([s1, s2], s3)
+
+        tm.assert_frame_equal(result, expected)
+
+        assert result.index.names == ["foo", "foo"]
+        assert result.columns.names == ["bar_col"]
+
+        # Column names duplicated
+        s1 = pd.Series(range(3), name="foo")
+        s2 = s1 + 1
+        s3 = pd.Series(range(3), name="bar_row")
+
+        expected = pd.crosstab(s3, [s1, s2.rename("bar")]).rename_axis(
+            columns={"bar": "foo"}, axis=1
+        )
+        result = pd.crosstab(s3, [s1, s2])
+
+        tm.assert_frame_equal(result, expected)
+
+        assert result.index.names == ["bar_row"]
+        assert result.columns.names == ["foo", "foo"]
 
     @pytest.mark.parametrize("names", [["a", ("b", "c")], [("a", "b"), "c"]])
     def test_crosstab_tuple_name(self, names):

From 2733c17d29960be7a0e00886adf650bfd3a8694b Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sat, 11 Apr 2020 13:46:37 -0400
Subject: [PATCH 20/36] Removed pd. reference in tests

---
 pandas/tests/reshape/test_crosstab.py | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/pandas/tests/reshape/test_crosstab.py b/pandas/tests/reshape/test_crosstab.py
index 6244051ad5f9e..129dc1f8e09ff 100644
--- a/pandas/tests/reshape/test_crosstab.py
+++ b/pandas/tests/reshape/test_crosstab.py
@@ -538,9 +538,9 @@ def test_crosstab_dup_index_names(self):
         # GH Issue: #22529, GH#13279
 
         # Duplicate name shared between rows and columns
-        s1 = pd.Series(range(3), name="foo")
+        s1 = Series(range(3), name="foo")
         s2 = s1 + 1
-        expected = pd.crosstab(s1, s2.rename("bar")).rename_axis(
+        expected = crosstab(s1, s2.rename("bar")).rename_axis(
             columns={"bar": "foo"}, axis=1
         )
         result = pd.crosstab(s1, s2)
@@ -549,14 +549,14 @@ def test_crosstab_dup_index_names(self):
         assert result.columns.names == ["foo"]
 
         # Row names duplicated
-        s1 = pd.Series(range(3), name="foo")
+        s1 = Series(range(3), name="foo")
         s2 = s1 + 1
-        s3 = pd.Series(range(3), name="bar_col")
+        s3 = Series(range(3), name="bar_col")
 
-        expected = pd.crosstab([s1, s2.rename("bar")], s3).rename_axis(
+        expected = crosstab([s1, s2.rename("bar")], s3).rename_axis(
             index={"bar": "foo"}, axis=0
         )
-        result = pd.crosstab([s1, s2], s3)
+        result = crosstab([s1, s2], s3)
 
         tm.assert_frame_equal(result, expected)
 
@@ -564,14 +564,14 @@ def test_crosstab_dup_index_names(self):
         assert result.columns.names == ["bar_col"]
 
         # Column names duplicated
-        s1 = pd.Series(range(3), name="foo")
+        s1 = Series(range(3), name="foo")
         s2 = s1 + 1
-        s3 = pd.Series(range(3), name="bar_row")
+        s3 = Series(range(3), name="bar_row")
 
-        expected = pd.crosstab(s3, [s1, s2.rename("bar")]).rename_axis(
+        expected = crosstab(s3, [s1, s2.rename("bar")]).rename_axis(
             columns={"bar": "foo"}, axis=1
         )
-        result = pd.crosstab(s3, [s1, s2])
+        result = crosstab(s3, [s1, s2])
 
         tm.assert_frame_equal(result, expected)
 

From f1b19a643cfebcd7751d046bbfa6ca14dde31b7d Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sat, 11 Apr 2020 13:46:56 -0400
Subject: [PATCH 21/36] Removed pd. reference in tests

---
 pandas/tests/reshape/test_crosstab.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/reshape/test_crosstab.py b/pandas/tests/reshape/test_crosstab.py
index 129dc1f8e09ff..b0298b910d206 100644
--- a/pandas/tests/reshape/test_crosstab.py
+++ b/pandas/tests/reshape/test_crosstab.py
@@ -543,7 +543,7 @@ def test_crosstab_dup_index_names(self):
         expected = crosstab(s1, s2.rename("bar")).rename_axis(
             columns={"bar": "foo"}, axis=1
         )
-        result = pd.crosstab(s1, s2)
+        result = crosstab(s1, s2)
         tm.assert_frame_equal(result, expected)
         assert result.index.names == ["foo"]
         assert result.columns.names == ["foo"]

From 85e010bffd2eefe2625e9f1c64091ea94ba54d85 Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Fri, 29 May 2020 19:27:05 -0400
Subject: [PATCH 22/36] Added Set import from typing

---
 pandas/core/reshape/pivot.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 5e1141e06ae2d..718db61db3698 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -5,6 +5,7 @@
     List,
     Optional,
     Sequence,
+    Set,
     Tuple,
     Union,
     cast,

From 3ed74d994991b965a61a2ea5d9983941a2ae44be Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sun, 12 Jul 2020 23:23:57 -0400
Subject: [PATCH 23/36] Renamed duplicated row/col names test

---
 pandas/tests/reshape/test_crosstab.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/tests/reshape/test_crosstab.py b/pandas/tests/reshape/test_crosstab.py
index b0298b910d206..2e21a55d97493 100644
--- a/pandas/tests/reshape/test_crosstab.py
+++ b/pandas/tests/reshape/test_crosstab.py
@@ -533,11 +533,11 @@ def test_crosstab_with_numpy_size(self):
         )
         tm.assert_frame_equal(result, expected)
 
-    def test_crosstab_dup_index_names(self):
-        # We test that duplicated column names do not produce issues
+    def test_crosstab_duplicated_row_and_col_names(self):
+        # We test that duplicated row or column names do not produce issues
         # GH Issue: #22529, GH#13279
 
-        # Duplicate name shared between rows and columns
+        # Same name in both rows and columns
         s1 = Series(range(3), name="foo")
         s2 = s1 + 1
         expected = crosstab(s1, s2.rename("bar")).rename_axis(

From e5c6cd953223548e8d7b537ac1e963d578f978de Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Sun, 12 Jul 2020 23:31:15 -0400
Subject: [PATCH 24/36] Added what's new entry

---
 doc/source/whatsnew/v1.1.0.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v1.1.0.rst b/doc/source/whatsnew/v1.1.0.rst
index 5f93e08d51baa..b92ae2161263d 100644
--- a/doc/source/whatsnew/v1.1.0.rst
+++ b/doc/source/whatsnew/v1.1.0.rst
@@ -1124,6 +1124,7 @@ Reshaping
 - Bug in :meth:`Series.where` with an empty Series and empty ``cond`` having non-bool dtype (:issue:`34592`)
 - Fixed regression where :meth:`DataFrame.apply` would raise ``ValueError`` for elements whth ``S`` dtype (:issue:`34529`)
 - Bug in :meth:`DataFrame.append` leading to sorting columns even when ``sort=False`` is specified (:issue:`35092`)
+- Bug in :meth:`DataFrame.crosstab` when duplicated row or column names were used (:issue:`22529`)
 
 Sparse
 ^^^^^^

From dc1d5c5ddb0df20c375dc005d314b87bbc0e0abd Mon Sep 17 00:00:00 2001
From: Fernando Irarrazaval <fbirarra@uc.cl>
Date: Fri, 11 Sep 2020 13:10:42 -0400
Subject: [PATCH 25/36] Updated reference to value_counts_arraylike

---
 pandas/core/reshape/pivot.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 8beb5e9503b51..fa34258f89439 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -20,7 +20,7 @@
 from pandas.core.dtypes.common import is_integer_dtype, is_list_like, is_scalar
 from pandas.core.dtypes.generic import ABCDataFrame, ABCSeries
 
-from pandas.core.algorithms import _value_counts_arraylike
+import pandas.core.algorithms as algos
 import pandas.core.common as com
 from pandas.core.frame import _shared_docs
 from pandas.core.groupby import Grouper
@@ -773,7 +773,7 @@ def _build_names_mapper(
     unique_names: list
         Unique names in the same order that names came in
     """
-    keys, counts = _value_counts_arraylike(names, dropna=False)
+    keys, counts = algos.value_counts_arraylike(names, dropna=False)
     names_count = dict(zip(keys, counts))
 
     names_mapper = {}

From 86c6ff1005ccd4fa7d017a5b37607fbe9f69f55b Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 06:45:26 +0000
Subject: [PATCH 26/36] consolidate test

---
 pandas/tests/reshape/test_crosstab.py | 44 +++++++--------------------
 1 file changed, 11 insertions(+), 33 deletions(-)

diff --git a/pandas/tests/reshape/test_crosstab.py b/pandas/tests/reshape/test_crosstab.py
index 1896d392b31a1..50b30cf8a73ac 100644
--- a/pandas/tests/reshape/test_crosstab.py
+++ b/pandas/tests/reshape/test_crosstab.py
@@ -536,50 +536,28 @@ def test_crosstab_with_numpy_size(self):
         tm.assert_frame_equal(result, expected)
 
     def test_crosstab_duplicated_row_and_col_names(self):
-        # We test that duplicated row or column names do not produce issues
-        # GH Issue: #22529, GH#13279
+        # GH22529
 
-        # Same name in both rows and columns
         s1 = Series(range(3), name="foo")
-        s2 = s1 + 1
-        expected = crosstab(s1, s2.rename("bar")).rename_axis(
-            columns={"bar": "foo"}, axis=1
-        )
-        result = crosstab(s1, s2)
-        tm.assert_frame_equal(result, expected)
-        assert result.index.names == ["foo"]
-        assert result.columns.names == ["foo"]
-
-        # Row names duplicated
-        s1 = Series(range(3), name="foo")
-        s2 = s1 + 1
-        s3 = Series(range(3), name="bar_col")
-
-        expected = crosstab([s1, s2.rename("bar")], s3).rename_axis(
-            index={"bar": "foo"}, axis=0
-        )
-        result = crosstab([s1, s2], s3)
+        s2_foo = Series(range(1, 4), name="foo")
+        s2_bar = Series(range(1, 4), name="bar")
+        s3 = Series(range(3), name="waldo")
 
+        result = crosstab(s1, s2_foo)
+        expected = crosstab(s1, s2_bar).rename_axis(columns={"bar": "foo"}, axis=1)
         tm.assert_frame_equal(result, expected)
 
-        assert result.index.names == ["foo", "foo"]
-        assert result.columns.names == ["bar_col"]
-
-        # Column names duplicated
-        s1 = Series(range(3), name="foo")
-        s2 = s1 + 1
-        s3 = Series(range(3), name="bar_row")
+        result = crosstab([s1, s2_foo], s3)
+        expected = crosstab([s1, s2_bar], s3).rename_axis(index={"bar": "foo"}, axis=0)
+        tm.assert_frame_equal(result, expected)
 
-        expected = crosstab(s3, [s1, s2.rename("bar")]).rename_axis(
+        result = crosstab(s3, [s1, s2_foo])
+        expected = crosstab(s3, [s1, s2_bar]).rename_axis(
             columns={"bar": "foo"}, axis=1
         )
-        result = crosstab(s3, [s1, s2])
 
         tm.assert_frame_equal(result, expected)
 
-        assert result.index.names == ["bar_row"]
-        assert result.columns.names == ["foo", "foo"]
-
     @pytest.mark.parametrize("names", [["a", ("b", "c")], [("a", "b"), "c"]])
     def test_crosstab_tuple_name(self, names):
         s1 = Series(range(3), name=names[0])

From bbf77575f7232d10b5ff9f9ef549e1faf728fb26 Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 06:51:57 +0000
Subject: [PATCH 27/36] comments + cleanup

---
 pandas/tests/reshape/test_crosstab.py | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/pandas/tests/reshape/test_crosstab.py b/pandas/tests/reshape/test_crosstab.py
index 50b30cf8a73ac..6faf64789c687 100644
--- a/pandas/tests/reshape/test_crosstab.py
+++ b/pandas/tests/reshape/test_crosstab.py
@@ -535,26 +535,31 @@ def test_crosstab_with_numpy_size(self):
         )
         tm.assert_frame_equal(result, expected)
 
-    def test_crosstab_duplicated_row_and_col_names(self):
-        # GH22529
+    def test_crosstab_duplicate_names(self):
+        # GH 13279 / 22529
 
         s1 = Series(range(3), name="foo")
         s2_foo = Series(range(1, 4), name="foo")
         s2_bar = Series(range(1, 4), name="bar")
         s3 = Series(range(3), name="waldo")
 
+        # check result computed with duplicate labels against
+        # result computed with unique labels, then relabelled
+        mapper = {"bar": "foo"}
+
+        # duplicate row, column labels
         result = crosstab(s1, s2_foo)
-        expected = crosstab(s1, s2_bar).rename_axis(columns={"bar": "foo"}, axis=1)
+        expected = crosstab(s1, s2_bar).rename_axis(columns=mapper, axis=1)
         tm.assert_frame_equal(result, expected)
 
+        # duplicate row, unique column labels
         result = crosstab([s1, s2_foo], s3)
-        expected = crosstab([s1, s2_bar], s3).rename_axis(index={"bar": "foo"}, axis=0)
+        expected = crosstab([s1, s2_bar], s3).rename_axis(index=mapper, axis=0)
         tm.assert_frame_equal(result, expected)
 
+        # unique row, duplicate column labels
         result = crosstab(s3, [s1, s2_foo])
-        expected = crosstab(s3, [s1, s2_bar]).rename_axis(
-            columns={"bar": "foo"}, axis=1
-        )
+        expected = crosstab(s3, [s1, s2_bar]).rename_axis(columns=mapper, axis=1)
 
         tm.assert_frame_equal(result, expected)
 

From 00f6ca30fcf8ee913dd8c97d7d56a2b0347c0d36 Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 17:00:07 +0000
Subject: [PATCH 28/36] rewrite _build_names_mapper for rownames, colnames args

---
 pandas/core/reshape/pivot.py | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 4b77d675e3f3a..19e05d2f3e42b 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -5,7 +5,6 @@
     List,
     Optional,
     Sequence,
-    Set,
     Tuple,
     Union,
     cast,
@@ -597,15 +596,9 @@ def crosstab(
     rownames = _get_names(index, rownames, prefix="row")
     colnames = _get_names(columns, colnames, prefix="col")
 
-    # We create our own mapping of row and columns names
-    # to prevent issues with duplicate columns/row names. GH Issue: #22529
-    shared_col_row_names = set(rownames).intersection(set(colnames))
-    row_names_mapper, unique_row_names = _build_names_mapper(
-        rownames, shared_col_row_names, "row"
-    )
-    col_names_mapper, unique_col_names = _build_names_mapper(
-        colnames, shared_col_row_names, "col"
-    )
+    # duplicate names mapped to unique names for pivot op
+    row_names_mapper, unique_row_names = _build_names_mapper(rownames, colnames, "row")
+    col_names_mapper, unique_col_names = _build_names_mapper(rownames, colnames, "col")
 
     from pandas import DataFrame
 
@@ -749,7 +742,7 @@ def _get_names(arrs, names, prefix: str = "row"):
 
 
 def _build_names_mapper(
-    names: List[str], shared_col_row_names: Set[str], suffix: str
+    rownames: List[str], colnames: List[str], suffix: str
 ) -> Tuple[Dict[str, str], List[str]]:
     """
     Given a list of row or column names, creates a mapper of unique names to
@@ -771,6 +764,8 @@ def _build_names_mapper(
     unique_names: list
         Unique names in the same order that names came in
     """
+    shared_col_row_names = set(rownames).intersection(set(colnames))
+    names = rownames if suffix == "row" else colnames
     keys, counts = algos.value_counts_arraylike(names, dropna=False)
     names_count = dict(zip(keys, counts))
 

From 2a414916ed5566c3279ec0790e935022bf0cec31 Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 17:52:45 +0000
Subject: [PATCH 29/36] simplify _build_names_mapper

---
 pandas/core/reshape/pivot.py | 84 ++++++++++++++----------------------
 1 file changed, 33 insertions(+), 51 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 19e05d2f3e42b..ce8ba5bbed1b2 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -19,7 +19,6 @@
 from pandas.core.dtypes.common import is_integer_dtype, is_list_like, is_scalar
 from pandas.core.dtypes.generic import ABCDataFrame, ABCSeries
 
-import pandas.core.algorithms as algos
 import pandas.core.common as com
 from pandas.core.frame import _shared_docs
 from pandas.core.groupby import Grouper
@@ -597,8 +596,12 @@ def crosstab(
     colnames = _get_names(columns, colnames, prefix="col")
 
     # duplicate names mapped to unique names for pivot op
-    row_names_mapper, unique_row_names = _build_names_mapper(rownames, colnames, "row")
-    col_names_mapper, unique_col_names = _build_names_mapper(rownames, colnames, "col")
+    (
+        row_names_mapper,
+        unique_row_names,
+        col_names_mapper,
+        unique_col_names,
+    ) = _build_names_mapper(rownames, colnames)
 
     from pandas import DataFrame
 
@@ -742,56 +745,35 @@ def _get_names(arrs, names, prefix: str = "row"):
 
 
 def _build_names_mapper(
-    rownames: List[str], colnames: List[str], suffix: str
+    rownames: List[str], colnames: List[str]
 ) -> Tuple[Dict[str, str], List[str]]:
-    """
-    Given a list of row or column names, creates a mapper of unique names to
-    column/row names.
-
-    Parameters
-    ----------
-    names : list
-        Names to be deduplicated.
-    shared_col_row_names : set or list
-        Values used both in rows and columns, so need additional deduplication.
-    suffix : str
-        Suffix to deduplicate values in shared_col_row_names
+    def get_duplicates(names):
+        seen = set()
+        return {name for name in names if name not in seen and not seen.add(name)}
 
-    Returns
-    -------
-    names_mapper: dict
-        The keys are the unique names and the values are the original names.
-    unique_names: list
-        Unique names in the same order that names came in
-    """
     shared_col_row_names = set(rownames).intersection(set(colnames))
-    names = rownames if suffix == "row" else colnames
-    keys, counts = algos.value_counts_arraylike(names, dropna=False)
-    names_count = dict(zip(keys, counts))
-
-    names_mapper = {}
-    unique_names: List[str] = []
-    # We reverse the names so the numbers are in the order given by the user
-    for name in reversed(names):
-        mapped_name = name
-        name_count = names_count[name]
-
-        # Adds a number if name is duplicated within columns/rows
-        if name_count > 1:
-            mapped_name = "{mapped_name}_{name_count}".format(
-                mapped_name=mapped_name, name_count=name_count
-            )
-            names_count[name] -= 1
-
-        # Add suffix name if column is shared between column and rows
-        if name in shared_col_row_names:
-            mapped_name = "{mapped_name}_{suffix}".format(
-                mapped_name=mapped_name, suffix=suffix
-            )
-
-        names_mapper[mapped_name] = name
+    duplicate_names = (
+        shared_col_row_names | get_duplicates(rownames) | get_duplicates(colnames)
+    )
 
-        # Creates a list of the new names in the original order
-        unique_names.insert(0, mapped_name)
+    rownames_mapper = {
+        f"row_{i}": rowname
+        for i, rowname in enumerate(rownames)
+        if rowname in duplicate_names
+    }
+    unique_rownames = [
+        f"row_{i}" if rowname in duplicate_names else rowname
+        for i, rowname in enumerate(rownames)
+    ]
+
+    colnames_mapper = {
+        f"col_{i}": colname
+        for i, colname in enumerate(colnames)
+        if colname in duplicate_names
+    }
+    unique_colnames = [
+        f"col_{i}" if colname in duplicate_names else colname
+        for i, colname in enumerate(colnames)
+    ]
 
-    return names_mapper, unique_names
+    return rownames_mapper, unique_rownames, colnames_mapper, unique_colnames

From 975af3e6e24266f7ba19416727531f82fe9f7d0b Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 17:59:54 +0000
Subject: [PATCH 30/36] rename row_names->rownames, col_names->colnames for
 consistency

---
 pandas/core/reshape/pivot.py | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index ce8ba5bbed1b2..97ace103fd97e 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -597,17 +597,17 @@ def crosstab(
 
     # duplicate names mapped to unique names for pivot op
     (
-        row_names_mapper,
-        unique_row_names,
-        col_names_mapper,
-        unique_col_names,
+        rownames_mapper,
+        unique_rownames,
+        colnames_mapper,
+        unique_colnames,
     ) = _build_names_mapper(rownames, colnames)
 
     from pandas import DataFrame
 
     data = {
-        **dict(zip(unique_row_names, index)),
-        **dict(zip(unique_col_names, columns)),
+        **dict(zip(unique_rownames, index)),
+        **dict(zip(unique_colnames, columns)),
     }
     df = DataFrame(data, index=common_idx)
     original_df_cols = df.columns
@@ -621,8 +621,8 @@ def crosstab(
 
     table = df.pivot_table(
         ["__dummy__"],
-        index=unique_row_names,
-        columns=unique_col_names,
+        index=unique_rownames,
+        columns=unique_colnames,
         margins=margins,
         margins_name=margins_name,
         dropna=dropna,
@@ -641,8 +641,8 @@ def crosstab(
             table, normalize=normalize, margins=margins, margins_name=margins_name
         )
 
-    table = table.rename_axis(index=row_names_mapper, axis=0)
-    table = table.rename_axis(columns=col_names_mapper, axis=1)
+    table = table.rename_axis(index=rownames_mapper, axis=0)
+    table = table.rename_axis(columns=colnames_mapper, axis=1)
 
     return table
 

From 33f76c8e1e365b3d52a4b6ac4a2ba786b66aa1b6 Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 18:04:43 +0000
Subject: [PATCH 31/36] rewrite whatsnew

---
 doc/source/whatsnew/v1.2.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v1.2.0.rst b/doc/source/whatsnew/v1.2.0.rst
index 54c9964b54918..a7854b66475f5 100644
--- a/doc/source/whatsnew/v1.2.0.rst
+++ b/doc/source/whatsnew/v1.2.0.rst
@@ -712,7 +712,7 @@ Groupby/resample/rolling
 Reshaping
 ^^^^^^^^^
 
-- Bug in :meth:`DataFrame.crosstab` when duplicated row or column names were used (:issue:`22529`)
+- Bug in :meth:`DataFrame.crosstab` was returning incorrect results on inputs with duplicate row names, duplicate column names or duplicate names between row and column labels (:issue:`22529`)
 - Bug in :meth:`DataFrame.pivot_table` with ``aggfunc='count'`` or ``aggfunc='sum'`` returning ``NaN`` for missing categories when pivoted on a ``Categorical``. Now returning ``0`` (:issue:`31422`)
 - Bug in :func:`union_indexes` where input index names are not preserved in some cases. Affects :func:`concat` and :class:`DataFrame` constructor (:issue:`13475`)
 - Bug in func :meth:`crosstab` when using multiple columns with ``margins=True`` and ``normalize=True`` (:issue:`35144`)

From c9a11dd9de08dee4ff6b2befd477c52a857c179a Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 18:12:07 +0000
Subject: [PATCH 32/36] rename vars in _build_names_mapper

---
 pandas/core/reshape/pivot.py | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 97ace103fd97e..c884877305f0f 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -747,33 +747,25 @@ def _get_names(arrs, names, prefix: str = "row"):
 def _build_names_mapper(
     rownames: List[str], colnames: List[str]
 ) -> Tuple[Dict[str, str], List[str]]:
-    def get_duplicates(names):
+    def duplicates(names):
         seen = set()
         return {name for name in names if name not in seen and not seen.add(name)}
 
-    shared_col_row_names = set(rownames).intersection(set(colnames))
-    duplicate_names = (
-        shared_col_row_names | get_duplicates(rownames) | get_duplicates(colnames)
-    )
+    shared_names = set(rownames).intersection(set(colnames))
+    duplicates = duplicates(rownames) | duplicates(colnames) | shared_names
 
     rownames_mapper = {
-        f"row_{i}": rowname
-        for i, rowname in enumerate(rownames)
-        if rowname in duplicate_names
+        f"row_{i}": name for i, name in enumerate(rownames) if name in duplicates
     }
     unique_rownames = [
-        f"row_{i}" if rowname in duplicate_names else rowname
-        for i, rowname in enumerate(rownames)
+        f"row_{i}" if name in duplicates else name for i, name in enumerate(rownames)
     ]
 
     colnames_mapper = {
-        f"col_{i}": colname
-        for i, colname in enumerate(colnames)
-        if colname in duplicate_names
+        f"col_{i}": name for i, name in enumerate(colnames) if name in duplicates
     }
     unique_colnames = [
-        f"col_{i}" if colname in duplicate_names else colname
-        for i, colname in enumerate(colnames)
+        f"col_{i}" if name in duplicates else name for i, name in enumerate(colnames)
     ]
 
     return rownames_mapper, unique_rownames, colnames_mapper, unique_colnames

From a8498844cbeec6602a368b99fa2c401e5a2758a9 Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 19:27:52 +0000
Subject: [PATCH 33/36] typing

---
 pandas/core/reshape/pivot.py | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index c884877305f0f..1eaf48ebb1de6 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -5,6 +5,7 @@
     List,
     Optional,
     Sequence,
+    Set,
     Tuple,
     Union,
     cast,
@@ -746,10 +747,10 @@ def _get_names(arrs, names, prefix: str = "row"):
 
 def _build_names_mapper(
     rownames: List[str], colnames: List[str]
-) -> Tuple[Dict[str, str], List[str]]:
+) -> Tuple[Dict[str, str], List[str], Dict[str, str], List[str]]:
     def duplicates(names):
-        seen = set()
-        return {name for name in names if name not in seen and not seen.add(name)}
+        seen: Set = set()
+        return {name for name in names if name not in seen}
 
     shared_names = set(rownames).intersection(set(colnames))
     duplicates = duplicates(rownames) | duplicates(colnames) | shared_names

From 0c44679b8720b11e409c454375a83601c6cc07cf Mon Sep 17 00:00:00 2001
From: arw2019 <andrew.r.wieteska@gmail.com>
Date: Sun, 22 Nov 2020 19:55:58 +0000
Subject: [PATCH 34/36] more typing

---
 pandas/core/reshape/pivot.py | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 1eaf48ebb1de6..860eccd859590 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -748,25 +748,25 @@ def _get_names(arrs, names, prefix: str = "row"):
 def _build_names_mapper(
     rownames: List[str], colnames: List[str]
 ) -> Tuple[Dict[str, str], List[str], Dict[str, str], List[str]]:
-    def duplicates(names):
+    def get_duplicates(names):
         seen: Set = set()
         return {name for name in names if name not in seen}
 
     shared_names = set(rownames).intersection(set(colnames))
-    duplicates = duplicates(rownames) | duplicates(colnames) | shared_names
+    dup_names = get_duplicates(rownames) | get_duplicates(colnames) | shared_names
 
     rownames_mapper = {
-        f"row_{i}": name for i, name in enumerate(rownames) if name in duplicates
+        f"row_{i}": name for i, name in enumerate(rownames) if name in dup_names
     }
     unique_rownames = [
-        f"row_{i}" if name in duplicates else name for i, name in enumerate(rownames)
+        f"row_{i}" if name in dup_names else name for i, name in enumerate(rownames)
     ]
 
     colnames_mapper = {
-        f"col_{i}": name for i, name in enumerate(colnames) if name in duplicates
+        f"col_{i}": name for i, name in enumerate(colnames) if name in dup_names
     }
     unique_colnames = [
-        f"col_{i}" if name in duplicates else name for i, name in enumerate(colnames)
+        f"col_{i}" if name in dup_names else name for i, name in enumerate(colnames)
     ]
 
     return rownames_mapper, unique_rownames, colnames_mapper, unique_colnames

From e42011a3041cb94b59dbd2733ef87d1aca74af29 Mon Sep 17 00:00:00 2001
From: Andrew Wieteska <andrew.r.wieteska@gmail.com>
Date: Thu, 26 Nov 2020 22:52:53 -0500
Subject: [PATCH 35/36] review comment: add docstring

---
 pandas/core/reshape/pivot.py | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index 860eccd859590..f84b0ef1c4932 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -748,6 +748,33 @@ def _get_names(arrs, names, prefix: str = "row"):
 def _build_names_mapper(
     rownames: List[str], colnames: List[str]
 ) -> Tuple[Dict[str, str], List[str], Dict[str, str], List[str]]:
+    """
+    Given the names of a DataFrame's rows and columns, returns a set of unique row
+    and column names and mappers that convert to original names.
+
+    A row or column name is replaced if it is duplicate among the rows of the inputs,
+    among the columns of the inputs or between the rows and the columns.
+
+    Paramters
+    ---------
+    rownames: list[str]
+    colnames: list[str]
+
+    Returns
+    -------
+    Tuple(Dict[str, str], List[str], Dict[str, str], List[str])
+
+    rownames_mapper:
+        a dictionary with new row names as keys and original rownames as values
+    unique_rownames:
+        a list of rownames with duplicate names replaced by dummy names
+    colnames_mapper:
+        a dictionary with new column names as keys and original column names as values
+    unique_colnames:
+        a list of column names with duplicate names replaced by dummy names
+
+    """
+
     def get_duplicates(names):
         seen: Set = set()
         return {name for name in names if name not in seen}

From 5ca044771d0a718a61e5a06309cdd3a3cc3ebe5d Mon Sep 17 00:00:00 2001
From: Andrew Wieteska <andrew.r.wieteska@gmail.com>
Date: Thu, 26 Nov 2020 22:53:58 -0500
Subject: [PATCH 36/36] more on docstring

---
 pandas/core/reshape/pivot.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pandas/core/reshape/pivot.py b/pandas/core/reshape/pivot.py
index f84b0ef1c4932..22887cede51ed 100644
--- a/pandas/core/reshape/pivot.py
+++ b/pandas/core/reshape/pivot.py
@@ -764,13 +764,13 @@ def _build_names_mapper(
     -------
     Tuple(Dict[str, str], List[str], Dict[str, str], List[str])
 
-    rownames_mapper:
+    rownames_mapper: dict[str, str]
         a dictionary with new row names as keys and original rownames as values
-    unique_rownames:
+    unique_rownames: list[str]
         a list of rownames with duplicate names replaced by dummy names
-    colnames_mapper:
+    colnames_mapper: dict[str, str]
         a dictionary with new column names as keys and original column names as values
-    unique_colnames:
+    unique_colnames: list[str]
         a list of column names with duplicate names replaced by dummy names
 
     """