BUG: don't allow to_panel to succeed if index is not unique. close #2441

Author: wesm

RELEASE.rst

@@ -140,6 +140,7 @@ pandas 0.10.0
   - Fix GroupBy.apply issue when using BinGrouper to do ts binning (#2300)
   - Fix issues resulting from datetime.datetime columns being converted to
     datetime64 when calling DataFrame.apply. (#2374)
+  - Raise exception when calling to_panel on non uniquely-indexed frame (#2441)
 
 
 pandas 0.9.1

pandas/core/frame.py

@@ -1200,6 +1200,10 @@ def to_panel(self):
             len(self.index.levels) != 2):
             raise AssertionError('Must have 2-level MultiIndex')
 
+        if not self.index.is_unique:
+            raise Exception("Can't convert non-uniquely indexed "
+                            "DataFrame to Panel")
+
         self._consolidate_inplace()
 
         # minor axis must be sorted

pandas/tests/test_panel.py

@@ -1128,6 +1128,12 @@ def test_to_panel_na_handling(self):
         panel = df.to_panel()
         self.assert_(isnull(panel[0].ix[1, [0, 1]]).all())
 
+    def test_to_panel_duplicates(self):
+        # #2441
+        df = DataFrame({'a': [0, 0, 1], 'b': [1, 1, 1], 'c': [1, 2, 3]})
+        idf = df.set_index(['a', 'b'])
+        self.assertRaises(Exception, idf.to_panel)
+
     def test_filter(self):
         pass