BUG: GH4516 Fixed issue with sorting a duplicate multi-index that has multiple dtypes

doc/source/release.rst

@@ -135,6 +135,7 @@ pandas 0.13
   - Raise on set indexing with a Panel and a Panel as a value which needs alignment (:issue:`3777`)
   - frozenset objects now raise in the ``Series`` constructor (:issue:`4482`,
     :issue:`4480`)
+  - Fixed issue with sorting a duplicate multi-index that has multiple dtypes (:issue:`4516`)
 
 pandas 0.12
 ===========

pandas/core/frame.py

@@ -3304,10 +3304,13 @@ def sortlevel(self, level=0, axis=0, ascending=True, inplace=False):
         new_axis, indexer = the_axis.sortlevel(level, ascending=ascending)
 
         if self._is_mixed_type and not inplace:
-            if axis == 0:
-                return self.reindex(index=new_axis)
+            ax = 'index' if axis == 0 else 'columns'
+
+            if new_axis.is_unique:
+                d = { ax : new_axis }
             else:
-                return self.reindex(columns=new_axis)
+                d = { ax : indexer, 'takeable' : True }
+            return self.reindex(**d)
 
         if inplace:
             if axis == 1:

pandas/core/index.py

@@ -2165,8 +2165,17 @@ def reindex(self, target, method=None, level=None, limit=None,
             if self.equals(target):
                 indexer = None
             else:
-                indexer = self.get_indexer(target, method=method,
-                                           limit=limit)
+                if self.is_unique:
+                    indexer = self.get_indexer(target, method=method,
+                                               limit=limit)
+                else:
+                    if takeable:
+                        if method is not None or limit is not None:
+                            raise ValueError("cannot do a takeable reindex with "
+                                             "with a method or limit")
+                        return self[target], target
+
+                    raise Exception("cannot handle a non-takeable non-unique multi-index!")
 
         if not isinstance(target, MultiIndex):
             if indexer is None:

pandas/tests/test_multilevel.py

@@ -1828,6 +1828,18 @@ def test_duplicate_groupby_issues(self):
         result = s.groupby(s.index).first()
         self.assertEquals(len(result), 3)
 
+    def test_duplicate_mi(self):
+        # GH 4516
+        df = DataFrame([['foo','bar',1.0,1],['foo','bar',2.0,2],['bah','bam',3.0,3],
+                        ['bah','bam',4.0,4],['foo','bar',5.0,5],['bah','bam',6.0,6]],
+                       columns=list('ABCD'))
+        df = df.set_index(['A','B'])
+        df = df.sortlevel(0)
+        result = df.loc[('foo','bar')]
+        expected = DataFrame([['foo','bar',1.0,1],['foo','bar',2.0,2],['foo','bar',5.0,5]],
+                             columns=list('ABCD')).set_index(['A','B'])
+        assert_frame_equal(result,expected)
+
     def test_multiindex_set_index(self):
         # segfault in #3308
         d = {'t1': [2, 2.5, 3], 't2': [4, 5, 6]}