Fix num_rows bug in batched_graph (#169)

python/dgl/batched_graph.py

@@ -31,12 +31,18 @@ class BatchedDGLGraph(DGLGraph):
         # create batched graph index
         batched_index = gi.disjoint_union([g._graph for g in graph_list])
         # create batched node and edge frames
+        if len(node_attrs) == 0:
+            batched_node_frame = FrameRef(Frame(num_rows=batched_index.number_of_nodes()))
+        else:
             # NOTE: following code will materialize the columns of the input graphs.
             cols = {key: F.cat([gr._node_frame[key] for gr in graph_list
                                 if gr.number_of_nodes() > 0], dim=0)
                     for key in node_attrs}
             batched_node_frame = FrameRef(Frame(cols))
 
+        if len(edge_attrs) == 0:
+            batched_edge_frame = FrameRef(Frame(num_rows=batched_index.number_of_edges()))
+        else:
             cols = {key: F.cat([gr._edge_frame[key] for gr in graph_list
                                 if gr.number_of_edges() > 0], dim=0)
                     for key in edge_attrs}

tests/pytorch/test_batched_graph.py

@@ -76,6 +76,20 @@ def test_batch_unbatch1():
     assert U.allclose(t2.ndata['h'], s3.ndata['h'])
     assert U.allclose(t2.edata['h'], s3.edata['h'])
 
+def test_batch_unbatch2():
+    # test setting/getting features after batch
+    a = dgl.DGLGraph()
+    a.add_nodes(4)
+    a.add_edges(0, [1, 2, 3])
+    b = dgl.DGLGraph()
+    b.add_nodes(3)
+    b.add_edges(0, [1, 2])
+    c = dgl.batch([a, b])
+    c.ndata['h'] = th.ones(7, 1)
+    c.edata['w'] = th.ones(5, 1)
+    assert U.allclose(c.ndata['h'], th.ones(7, 1))
+    assert U.allclose(c.edata['w'], th.ones(5, 1))
+
 def test_batch_send_then_recv():
     t1 = tree1()
     t2 = tree2()
@@ -166,6 +180,7 @@ def test_batch_no_edge():
 if __name__ == '__main__':
     test_batch_unbatch()
     test_batch_unbatch1()
+    test_batch_unbatch2()
     test_batched_edge_ordering()
     test_batch_send_then_recv()
     test_batch_send_and_recv()