add negative sampling demo for DTDG

demo_dtdg.py

@@ -49,6 +49,7 @@ def prepare_data(root: str, num_parts):
     g.node()["y"] = y
     g.edge()["time"] = edge_times
     g.edge()["attr"] = edge_attr
+    g.meta()["num_nodes"] = x.size(0) # 全局的节点数量
     g.meta()["num_snapshots"] = snapshot_count # 快照数量
 
     logging.info(f"GraphData.meta().keys(): {g.meta().keys()}")
@@ -289,8 +290,6 @@ def get_graph(
     
     sg = GraphData.from_bipartite(
         edge_index=edge_index,
-        num_src_nodes=g.node("src").num_nodes,
-        num_dst_nodes=g.node("dst").num_nodes,
         raw_src_ids=g.node("src")["raw_ids"],
         raw_dst_ids=g.node("dst")["raw_ids"],
     )
@@ -299,8 +298,31 @@ def get_graph(
     sg.edge()["time"] = time[mask] - start # 快照偏移从0开始
     sg.edge()["attr"] = edge_attr
     sg.meta()["num_snapshots"] = end - start
+    sg.meta()["num_nodes"] = g.meta()["num_nodes"]
     return sg
 
+def get_negative_route(g: GraphData, num_edges: int, group: Any):
+    num_nodes = g.meta()["num_nodes"] # 这个num_nodes是全局节点数量
+    raw_src_ids = g.node("src")["raw_ids"]
+    raw_dst_ids = g.node("dst")["raw_ids"]
+
+    # 随机选择src节点
+    src = torch.randint(num_nodes, size=(num_edges,)).type_as(raw_src_ids)
+
+    # 随机选择dst节点，并映射到全局id
+    dst = torch.randint(raw_dst_ids.numel(), size=(num_edges,)).type_as(raw_dst_ids)
+    dst = raw_dst_ids[dst]
+
+    edge_index = torch.vstack([src, dst]) # 生成负采样边
+    raw_src_ids = src.unique() # 对src节点去重，raw_dst_ids本身就是去重的
+
+    route = GraphData.from_bipartite(
+        edge_index=edge_index,
+        raw_src_ids=raw_src_ids,
+        raw_dst_ids=raw_dst_ids,
+    ).to_route(group)
+    return route, edge_index
+
 if __name__ == "__main__":
     data_root = "./dataset"
     
@@ -407,3 +429,9 @@ if __name__ == "__main__":
 
         opt.step()
         ctx.sync_print(f"loss: {loss.item():.6f}")
+
+    if True:
+        """案例4：随机负采样边及其route。保持dst节点不变，随机选择src节点
+        """
+        route, edge_index = get_negative_route(g, num_edges=1000, group=pp_group)
+        ctx.sync_print(route, edge_index.size())
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