BUG: raise exception when view not possible of multiindex'd dataframe. close #2117

Author: wesm

RELEASE.rst

@@ -68,6 +68,7 @@ pandas 0.9.1
   - Work around length-0 boolean indexing NumPy bug (#2096)
   - Fix partial integer indexing bug in DataFrame.xs (#2107)
   - Fix variety of cut/qcut string-bin formatting bugs (#1978, #1979)
+  - Raise Exception when xs view not possible of MultiIndex'd DataFrame (#2117)
 
 pandas 0.9.0
 ============

pandas/core/frame.py

@@ -2018,6 +2018,9 @@ def xs(self, key, axis=0, level=None, copy=True):
         if level is not None:
             loc, new_ax = labels.get_loc_level(key, level=level)
 
+            if not copy and not isinstance(loc, slice):
+                raise ValueError('Cannot retrieve view (copy=False)')
+
             # level = 0
             if not isinstance(loc, slice):
                 indexer = [slice(None, None)] * 2

pandas/tests/test_multilevel.py

@@ -1555,6 +1555,14 @@ def test_indexing_over_hashtable_size_cutoff(self):
 
         lib._SIZE_CUTOFF = old_cutoff
 
+    def test_xs_mixed_no_copy(self):
+        index = MultiIndex.from_arrays([['a','a', 'b', 'b'], [1,2,1,2]],
+                                       names=['first', 'second'])
+        data = DataFrame(np.random.rand(len(index)), index=index,
+                         columns=['A'])
+
+        self.assertRaises(Exception, data.xs, 2, level=1, copy=False)
+
 if __name__ == '__main__':
 
     # unittest.main()