BUG: Bug in loc setting with multiple indexers and a rhs of a Series that needs broadcasting (GH5206)

doc/source/release.rst

@@ -594,6 +594,8 @@ Bug Fixes
   - Bug in comparing duplicate frames (:issue:`4421`) related
   - Bug in describe on duplicate frames
   - Bug in ``to_datetime`` with a format and ``coerce=True`` not raising (:issue:`5195`)
+  - Bug in ``loc`` setting with multiple indexers and a rhs of a Series that needs
+    broadcasting (:issue:`5206`)
 
 pandas 0.12.0
 -------------

pandas/core/indexing.py

@@ -370,9 +370,11 @@ def _align_series(self, indexer, ser):
         if isinstance(indexer, tuple):
 
             aligners = [ not _is_null_slice(idx) for idx in indexer ]
-            single_aligner = sum(aligners) == 1
+            sum_aligners = sum(aligners)
+            single_aligner = sum_aligners == 1
             is_frame = self.obj.ndim == 2
             is_panel = self.obj.ndim >= 3
+            obj = self.obj
 
             # are we a single alignable value on a non-primary
             # dim (e.g. panel: 1,2, or frame: 0) ?
@@ -387,7 +389,15 @@ def _align_series(self, indexer, ser):
             elif is_panel:
                 single_aligner = single_aligner and (aligners[1] or aligners[2])
 
-            obj = self.obj
+            # we have a frame, with multiple indexers on both axes; and a series,
+            # so need to broadcast (see GH5206)
+            if sum_aligners == self.ndim and 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
+                return ser
+
             for i, idx in enumerate(indexer):
                 ax = obj.axes[i]
 
@@ -398,6 +408,8 @@ def _align_series(self, indexer, ser):
                     new_ix = ax[idx]
                     if not is_list_like(new_ix):
                         new_ix = Index([new_ix])
+                    else:
+                        new_ix = Index(new_ix.ravel())
                     if ser.index.equals(new_ix):
                         return ser.values.copy()
                     return ser.reindex(new_ix).values

pandas/tests/test_indexing.py

@@ -1037,6 +1037,17 @@ def test_multi_assign(self):
         df2.ix[mask, cols]= dft.ix[mask, cols].values
         assert_frame_equal(df2,expected)
 
+        # broadcasting on the rhs is required
+        df = DataFrame(dict(A = [1,2,0,0,0],B=[0,0,0,10,11],C=[0,0,0,10,11],D=[3,4,5,6,7]))
+
+        expected = df.copy()
+        mask = expected['A'] == 0
+        for col in ['A','B']:
+            expected.loc[mask,col] = df['D']
+
+        df.loc[df['A']==0,['A','B']] = df['D']
+        assert_frame_equal(df,expected)
+
     def test_ix_assign_column_mixed(self):
         # GH #1142
         df = DataFrame(tm.getSeriesData())