[Bugfix][MetaPath2Vec]Fix MetaPath2Vec sample function bug (Issue #5514) #7875
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When a node has no neighbors according to the meta-path, the random walk from `dgl.sampling` will generate a node with id -1. When transforming the local node id to global node id, it incorrectly maps to the last node with the same type, resulting in non-existent paths. By filtering out invalid nodes (i.e., nodes with id -1) in the random walk process, non-existent paths are avoided. The new sample function introduces two edge cases: 1. Sampling with 0 pairs of nodes, which generates an empty tensor, leading to a NaN loss in the model’s forward function. This is handled by checking and returning a loss of 0.0 to prevent errors when there are no valid positive samples. Returning a loss of 0.0 ensures that the forward pass is unaffected and prevents unnecessary computation. 2. Sampling with only 1 pair of nodes, where the `neg_score` calculation is modified to use `.squeeze(-1)` to correctly handle the dimension.
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Description
In the
MetaPath2Vecsamplefunction,dgl.sampling.random_walkgenerates node ID-1when there are no neighbors following the given meta-path. For example, a sampled path may look like:[user_0, company_1, product_-1, company_-1, user_-1]
When mapping these local node IDs to global node IDs, the path becomes:
[10, 1, 9, 4, 14]
However, the sub-path
[9, 14]does not actually exist in the graph, leading to incorrect edge relationships.Fix
By filtering out
-1nodes generated byrandom_walk, the issue of non-existent paths is resolved. However, this introduces an edge case where certain nodes (e.g., nodes13and14in the example graph) have no valid neighbors for the first edge. In such cases, the path length is1, meaning thesamplefunction does not generate any valid node pairs.To handle this case, the model's
forwardfunction is modified to return a loss of0.0when there are no valid positive samples. This prevents errors and ensures the backward pass remains unaffected.Checklist
Please feel free to remove inapplicable items for your PR.