Merge pull request #6799 from jreback/iloc_dups_1

BUG: duplicate (getitem) indexing with iloc (GH6766)

Author: jreback

pandas/core/internals.py

@@ -674,7 +674,8 @@ def setitem(self, indexer, value):
             values = self._try_coerce_result(values)
             values = self._try_cast_result(values, dtype)
             return [make_block(transf(values), self.items, self.ref_items,
-                               ndim=self.ndim, fastpath=True)]
+                               ndim=self.ndim, placement=self._ref_locs,
+                               fastpath=True)]
         except (ValueError, TypeError) as detail:
             raise
         except Exception as detail:
@@ -2902,7 +2903,10 @@ def fast_xs(self, loc, copy=False):
 
         # non-unique (GH4726)
         if not items.is_unique:
-            return self._interleave(items).ravel(), True
+            result = self._interleave(items)
+            if self.ndim == 2:
+                result = result.T
+            return result[loc], True
 
         # unique
         dtype = _interleaved_dtype(self.blocks)

pandas/tests/test_indexing.py

@@ -483,6 +483,19 @@ def test_iloc_getitem_dups(self):
         # no dups in panel (bug?)
         self.check_result('list int (dups)', 'iloc', [0,1,1,3], 'ix', { 0 : [0,2,2,6], 1 : [0,3,3,9] }, objs = ['series','frame'], typs = ['ints'])
 
+        # GH 6766
+        df1 = DataFrame([{'A':None, 'B':1},{'A':2, 'B':2}])
+        df2 = DataFrame([{'A':3, 'B':3},{'A':4, 'B':4}])
+        df = concat([df1, df2], axis=1)
+
+        # cross-sectional indexing
+        result = df.iloc[0,0]
+        self.assertTrue(isnull(result))
+
+        result = df.iloc[0,:]
+        expected = Series([np.nan,1,3,3],index=['A','B','A','B'])
+        assert_series_equal(result,expected)
+
     def test_iloc_getitem_array(self):
 
         # array like