Link-level `NeighborLoader`

🚀 The feature, motivation and pitch

Currently, NeighborLoader is designed to be applied in node-level tasks and there exists no option for mini-batching in link-level tasks.

To achieve this, users currently rely on a simple but hacky workaround, first utilized in ogbl-citation2 in this example.

The idea is straightforward and simple: For input_nodes, we pass in both the source and destination nodes for every link we want to do link prediction on (both positive and negative):

loader = NeighborLoader(data, input_nodes=edge_label_index.view(-1), ...)

Nonetheless, PyG should provide a dedicated class to perform mini-batch on link-level tasks, re-using functionality from NeighborLoader under-the-hood. An API could look like:

class LinkLevelNeighborLoader(
    data,
     input_edges=...
     input_edge_labels=...
     with_negative_sampling=True,
     **kwargs,
)

NOTE: This workaround currently only works for homogenous graphs!

@RexYing @JiaxuanYou

[rusty1s]

We will post here once we make progress. Sorry for the delay.

[rusty1s]

You need to install PyG master or from nightly.