Fix RuntimeError in maybe_num_nodes_dict with empty edge indices from #10386

test/utils/test_num_nodes.py

@@ -30,3 +30,31 @@ def test_maybe_num_nodes_dict():
         '1': 3,
         '2': 6,
     }
+
+
+def test_maybe_num_nodes_dict_empty_edge_index():
+    # Test with empty edge indices (regression test for bug fix)
+    edge_index_dict = {
+        ('user', 'rates', 'movie'):
+        torch.tensor([[], []], dtype=torch.long),
+        ('user', 'follows', 'user'):
+        torch.tensor([[0, 1], [1, 2]], dtype=torch.long),
+    }
+
+    result = maybe_num_nodes_dict(edge_index_dict)
+    assert result == {'user': 3, 'movie': 0}
+
+    # Test with all empty edge indices
+    edge_index_dict_all_empty = {
+        ('user', 'rates', 'movie'): torch.tensor([[], []], dtype=torch.long),
+        ('movie', 'in', 'genre'): torch.tensor([[], []], dtype=torch.long),
+    }
+
+    result_all_empty = maybe_num_nodes_dict(edge_index_dict_all_empty)
+    assert result_all_empty == {'user': 0, 'movie': 0, 'genre': 0}
+
+    # Test with provided num_nodes_dict and empty edges
+    num_nodes_dict = {'movie': 10}
+    result_with_provided = maybe_num_nodes_dict(edge_index_dict,
+                                                num_nodes_dict)
+    assert result_with_provided == {'user': 3, 'movie': 10}

torch_geometric/utils/num_nodes.py

@@ -52,12 +52,14 @@ def maybe_num_nodes_dict(
 
         key = keys[0]
         if key not in found_types:
-            N = int(edge_index[0].max() + 1)
+            N = int(edge_index[0].max() +
+                    1) if edge_index[0].numel() > 0 else 0
             num_nodes_dict[key] = max(N, num_nodes_dict.get(key, N))
 
         key = keys[-1]
         if key not in found_types:
-            N = int(edge_index[1].max() + 1)
+            N = int(edge_index[1].max() +
+                    1) if edge_index[1].numel() > 0 else 0
             num_nodes_dict[key] = max(N, num_nodes_dict.get(key, N))
 
     return num_nodes_dict