BUG: bug in chained assignment with ix and another chained series (GH5928)

doc/source/release.rst

@@ -88,6 +88,7 @@ Bug Fixes
   - Bug in fully reindexing a Panel (:issue:`5905`)
   - Bug in idxmin/max with object dtypes (:issue:`5914`)
   - Bug in ``BusinessDay`` when adding n days to a date not on offset when n>5 and n%5==0 (:issue:`5890`)
+  - Bug in assigning to chained series with a series via ix (:issue:`5928`)
 
 pandas 0.13.0
 -------------

pandas/core/indexing.py

@@ -421,7 +421,7 @@ def can_do_equal_len():
 
     def _align_series(self, indexer, ser):
         # indexer to assign Series can be tuple, slice, scalar
-        if isinstance(indexer, slice):
+        if isinstance(indexer, (slice, np.ndarray, list)):
             indexer = tuple([indexer])
 
         if isinstance(indexer, tuple):
@@ -453,8 +453,12 @@ def _align_series(self, indexer, ser):
                     all([com._is_sequence(_) for _ in indexer])):
                 ser = ser.reindex(obj.axes[0][indexer[0].ravel()],
                                   copy=True).values
-                l = len(indexer[1].ravel())
-                ser = np.tile(ser, l).reshape(l, -1).T
+
+                # single indexer
+                if len(indexer) > 1:
+                    l = len(indexer[1].ravel())
+                    ser = np.tile(ser, l).reshape(l, -1).T
+
                 return ser
 
             for i, idx in enumerate(indexer):

pandas/tests/test_indexing.py

@@ -476,6 +476,20 @@ def test_loc_setitem(self):
         expected = Series([1,1,0],index=[4,5,6])
         assert_series_equal(s, expected)
 
+        # GH 5928
+        # chained indexing assignment
+        df = DataFrame({'a' : [0,1,2] })
+        expected = df.copy()
+        expected.ix[[0,1,2],'a'] = -expected.ix[[0,1,2],'a']
+
+        df['a'].ix[[0,1,2]] = -df['a'].ix[[0,1,2]]
+        assert_frame_equal(df,expected)
+
+        df = DataFrame({'a' : [0,1,2], 'b' :[0,1,2] })
+        df['a'].ix[[0,1,2]] = -df['a'].ix[[0,1,2]].astype('float64') + 0.5
+        expected = DataFrame({'a' : [0.5,-0.5,-1.5], 'b' : [0,1,2] })
+        assert_frame_equal(df,expected)
+
     def test_loc_getitem_int(self):
 
         # int label