NeighborSampler

class dgl.dataloading.NeighborSampler(fanouts, edge_dir='in', prob=None, mask=None, replace=False, prefetch_node_feats=None, prefetch_labels=None, prefetch_edge_feats=None, output_device=None)[source]

Bases: dgl.dataloading.base.BlockSampler

Sampler that builds computational dependency of node representations via neighbor sampling for multilayer GNN.

This sampler will make every node gather messages from a fixed number of neighbors per edge type. The neighbors are picked uniformly.

Parameters

  • fanouts (list[int] or list[dict[etype, int]]) –

    List of neighbors to sample per edge type for each GNN layer, with the i-th element being the fanout for the i-th GNN layer.

    If only a single integer is provided, DGL assumes that every edge type will have the same fanout.

    If -1 is provided for one edge type on one layer, then all inbound edges of that edge type will be included.

  • edge_dir (str, default 'in') – Can be either 'in' `` where the neighbors will be sampled according to incoming edges, or ``'out' otherwise, same as dgl.sampling.sample_neighbors().

  • prob (str, optional) –

    If given, the probability of each neighbor being sampled is proportional to the edge feature value with the given name in g.edata. The feature must be a scalar on each edge.

    This argument is mutually exclusive with mask. If you want to specify both a mask and a probability, consider multiplying the probability with the mask instead.

  • mask (str, optional) –

    If given, a neighbor could be picked only if the edge mask with the given name in g.edata is True. The data must be boolean on each edge.

    This argument is mutually exclusive with prob. If you want to specify both a mask and a probability, consider multiplying the probability with the mask instead.

  • replace (bool, default False) – Whether to sample with replacement

  • prefetch_node_feats (list[str] or dict[ntype, list[str]], optional) – The source node data to prefetch for the first MFG, corresponding to the input node features necessary for the first GNN layer.

  • prefetch_labels (list[str] or dict[ntype, list[str]], optional) – The destination node data to prefetch for the last MFG, corresponding to the node labels of the minibatch.

  • prefetch_edge_feats (list[str] or dict[etype, list[str]], optional) – The edge data names to prefetch for all the MFGs, corresponding to the edge features necessary for all GNN layers.

  • output_device (device, optional) – The device of the output subgraphs or MFGs. Default is the same as the minibatch of seed nodes.

Examples

Node classification

To train a 3-layer GNN for node classification on a set of nodes train_nid on a homogeneous graph where each node takes messages from 5, 10, 15 neighbors for the first, second, and third layer respectively (assuming the backend is PyTorch):

>>> sampler = dgl.dataloading.NeighborSampler([5, 10, 15])
>>> dataloader = dgl.dataloading.DataLoader(
...     g, train_nid, sampler,
...     batch_size=1024, shuffle=True, drop_last=False, num_workers=4)
>>> for input_nodes, output_nodes, blocks in dataloader:
...     train_on(blocks)

If training on a heterogeneous graph and you want different number of neighbors for each edge type, one should instead provide a list of dicts. Each dict would specify the number of neighbors to pick per edge type.

>>> sampler = dgl.dataloading.NeighborSampler([
...     {('user', 'follows', 'user'): 5,
...      ('user', 'plays', 'game'): 4,
...      ('game', 'played-by', 'user'): 3}] * 3)

If you would like non-uniform neighbor sampling:

>>> g.edata['p'] = torch.rand(g.num_edges())   # any non-negative 1D vector works
>>> sampler = dgl.dataloading.NeighborSampler([5, 10, 15], prob='p')

Or sampling on edge masks:

>>> g.edata['mask'] = torch.rand(g.num_edges()) < 0.2   # any 1D boolean mask works
>>> sampler = dgl.dataloading.NeighborSampler([5, 10, 15], prob='mask')

Edge classification and link prediction

This class can also work for edge classification and link prediction together with as_edge_prediction_sampler().

>>> sampler = dgl.dataloading.NeighborSampler([5, 10, 15])
>>> sampler = dgl.dataloading.as_edge_prediction_sampler(sampler)
>>> dataloader = dgl.dataloading.DataLoader(
...     g, train_eid, sampler,
...     batch_size=1024, shuffle=True, drop_last=False, num_workers=4)

See the documentation as_edge_prediction_sampler() for more details.

Notes

For the concept of MFGs, please refer to User Guide Section 6 and Minibatch Training Tutorials.