[BUG] Fix remove_edges crashing with empty edge ID tensors (dmlc#1384)

python/dgl/transform.py

@@ -922,15 +922,20 @@ def remove_edges(g, edge_ids):
                 "Graph has more than one edge type; specify a dict for edge_id instead.")
         edge_ids = {g.canonical_etypes[0]: edge_ids}
 
-    edge_ids_nd = [None] * len(g.etypes)
+    edge_ids_nd = [nd.null()] * len(g.etypes)
     for key, value in edge_ids.items():
         edge_ids_nd[g.get_etype_id(key)] = F.zerocopy_to_dgl_ndarray(value)
     new_graph_index, induced_eids_nd = _CAPI_DGLRemoveEdges(g._graph, edge_ids_nd)
 
     new_graph = DGLHeteroGraph(new_graph_index, g.ntypes, g.etypes)
     for i, canonical_etype in enumerate(g.canonical_etypes):
-        new_graph.edges[canonical_etype].data[EID] = F.zerocopy_from_dgl_ndarray(
-            induced_eids_nd[i].data)
+        data = induced_eids_nd[i].data
+        if len(data) == 0:
+            # Empty means that no edges are removed and edges are not shuffled.
+            new_graph.edges[canonical_etype].data[EID] = F.arange(
+                0, g.number_of_edges(canonical_etype))
+        else:
+            new_graph.edges[canonical_etype].data[EID] = F.zerocopy_from_dgl_ndarray(data)
 
     return new_graph
 

tests/compute/test_transform.py

@@ -542,6 +542,16 @@ def check(g1, etype, g, edges_removed):
     check(g2, 'AB', g, [3])
     check(g2, 'BA', g, [1])
 
+    g3 = dgl.remove_edges(g, {'AA': F.tensor([]), 'AB': F.tensor([3]), 'BA': F.tensor([1])})
+    check(g3, 'AA', g, [])
+    check(g3, 'AB', g, [3])
+    check(g3, 'BA', g, [1])
+
+    g4 = dgl.remove_edges(g, {'AB': F.tensor([3])})
+    check(g4, 'AA', g, [])
+    check(g4, 'AB', g, [3])
+    check(g4, 'BA', g, [])
+
 if __name__ == '__main__':
     test_line_graph()
     test_no_backtracking()