From 96938c4cdd5b207631b5c2976c42947ce0caaa68 Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Tue, 4 Sep 2018 16:51:49 +0100
Subject: [PATCH 1/2] TST: add test for GH6131

---
 pandas/tests/io/formats/test_to_html.py | 58 +++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/pandas/tests/io/formats/test_to_html.py b/pandas/tests/io/formats/test_to_html.py
index f69cac62513d4..0d80ef460c748 100644
--- a/pandas/tests/io/formats/test_to_html.py
+++ b/pandas/tests/io/formats/test_to_html.py
@@ -1844,6 +1844,64 @@ def test_to_html_no_index_max_rows(self):
         </table>""")
         assert result == expected
 
+    def test_to_html_pivot_table_max_cols(self):
+        # GH https://github.com/pandas-dev/pandas/issues/6131
+        df = DataFrame([
+            {'a': 'aa', 'b': 'ba', 'c': 'ca', 'd': 1},
+            {'a': 'ab', 'b': 'bb', 'c': 'cc', 'd': 2},
+            {'a': 'ac', 'b': 'bc', 'c': 'cc', 'd': 3}
+        ])
+        result = df.pivot_table(
+            columns=['a'], index=['b', 'c']).to_html(max_cols=2)
+        expected = dedent("""\
+        <table border="1" class="dataframe">
+          <thead>
+            <tr>
+              <th></th>
+              <th></th>
+              <th colspan="3" halign="left">d</th>
+            </tr>
+            <tr>
+              <th></th>
+              <th>a</th>
+              <th>aa</th>
+              <th>...</th>
+              <th>ac</th>
+            </tr>
+            <tr>
+              <th>b</th>
+              <th>c</th>
+              <th></th>
+              <th></th>
+              <th></th>
+            </tr>
+          </thead>
+          <tbody>
+            <tr>
+              <th>ba</th>
+              <th>ca</th>
+              <td>1.0</td>
+              <td>...</td>
+              <td>NaN</td>
+            </tr>
+            <tr>
+              <th>bb</th>
+              <th>cc</th>
+              <td>NaN</td>
+              <td>...</td>
+              <td>NaN</td>
+            </tr>
+            <tr>
+              <th>bc</th>
+              <th>cc</th>
+              <td>NaN</td>
+              <td>...</td>
+              <td>3.0</td>
+            </tr>
+          </tbody>
+        </table>""")
+        assert result == expected
+
     def test_to_html_notebook_has_style(self):
         df = pd.DataFrame({"A": [1, 2, 3]})
         result = df.to_html(notebook=True)

From 2d9c48fe011c71244ae0fb32f564b6c8d9269cb2 Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Sat, 8 Sep 2018 23:16:48 +0100
Subject: [PATCH 2/2] create result of pivot_table example explicitly

---
 pandas/tests/io/formats/test_to_html.py | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/pandas/tests/io/formats/test_to_html.py b/pandas/tests/io/formats/test_to_html.py
index 0d80ef460c748..845fb1ee3dc3a 100644
--- a/pandas/tests/io/formats/test_to_html.py
+++ b/pandas/tests/io/formats/test_to_html.py
@@ -1844,15 +1844,18 @@ def test_to_html_no_index_max_rows(self):
         </table>""")
         assert result == expected
 
-    def test_to_html_pivot_table_max_cols(self):
-        # GH https://github.com/pandas-dev/pandas/issues/6131
-        df = DataFrame([
-            {'a': 'aa', 'b': 'ba', 'c': 'ca', 'd': 1},
-            {'a': 'ab', 'b': 'bb', 'c': 'cc', 'd': 2},
-            {'a': 'ac', 'b': 'bc', 'c': 'cc', 'd': 3}
-        ])
-        result = df.pivot_table(
-            columns=['a'], index=['b', 'c']).to_html(max_cols=2)
+    def test_to_html_multiindex_max_cols(self):
+        # GH 6131
+        index = MultiIndex(levels=[['ba', 'bb', 'bc'], ['ca', 'cb', 'cc']],
+                           labels=[[0, 1, 2], [0, 1, 2]],
+                           names=['b', 'c'])
+        columns = MultiIndex(levels=[['d'], ['aa', 'ab', 'ac']],
+                             labels=[[0, 0, 0], [0, 1, 2]],
+                             names=[None, 'a'])
+        data = np.array(
+            [[1., np.nan, np.nan], [np.nan, 2., np.nan], [np.nan, np.nan, 3.]])
+        df = DataFrame(data, index, columns)
+        result = df.to_html(max_cols=2)
         expected = dedent("""\
         <table border="1" class="dataframe">
           <thead>
@@ -1886,7 +1889,7 @@ def test_to_html_pivot_table_max_cols(self):
             </tr>
             <tr>
               <th>bb</th>
-              <th>cc</th>
+              <th>cb</th>
               <td>NaN</td>
               <td>...</td>
               <td>NaN</td>