Source code for dgl.dataloading.graphsaint

"""GraphSAINT samplers."""
from ..base import DGLError
from ..random import choice
from ..sampling import pack_traces, random_walk
from .base import Sampler, set_edge_lazy_features, set_node_lazy_features

    import torch
except ImportError:

[docs]class SAINTSampler(Sampler): """Random node/edge/walk sampler from `GraphSAINT: Graph Sampling Based Inductive Learning Method <>`__ For each call, the sampler samples a node subset and then returns a node induced subgraph. There are three options for sampling node subsets: - For :attr:`'node'` sampler, the probability to sample a node is in proportion to its out-degree. - The :attr:`'edge'` sampler first samples an edge subset and then use the end nodes of the edges. - The :attr:`'walk'` sampler uses the nodes visited by random walks. It uniformly selects a number of root nodes and then performs a fixed-length random walk from each root node. Parameters ---------- mode : str The sampler to use, which can be :attr:`'node'`, :attr:`'edge'`, or :attr:`'walk'`. budget : int or tuple[int] Sampler configuration. - For :attr:`'node'` sampler, budget specifies the number of nodes in each sampled subgraph. - For :attr:`'edge'` sampler, budget specifies the number of edges to sample for inducing a subgraph. - For :attr:`'walk'` sampler, budget is a tuple. budget[0] specifies the number of root nodes to generate random walks. budget[1] specifies the length of a random walk. cache : bool, optional If False, it will not cache the probability arrays for sampling. Setting it to False is required if you want to use the sampler across different graphs. prefetch_ndata : list[str], optional The node data to prefetch for the subgraph. See :ref:`guide-minibatch-prefetching` for a detailed explanation of prefetching. prefetch_edata : list[str], optional The edge data to prefetch for the subgraph. See :ref:`guide-minibatch-prefetching` for a detailed explanation of prefetching. output_device : device, optional The device of the output subgraphs. Examples -------- >>> import torch >>> from dgl.dataloading import SAINTSampler, DataLoader >>> num_iters = 1000 >>> sampler = SAINTSampler(mode='node', budget=6000) >>> # Assume g.ndata['feat'] and g.ndata['label'] hold node features and labels >>> dataloader = DataLoader(g, torch.arange(num_iters), sampler, num_workers=4) >>> for subg in dataloader: ... train_on(subg) """ def __init__( self, mode, budget, cache=True, prefetch_ndata=None, prefetch_edata=None, output_device="cpu", ): super().__init__() self.budget = budget if mode == "node": self.sampler = self.node_sampler elif mode == "edge": self.sampler = self.edge_sampler elif mode == "walk": self.sampler = self.walk_sampler else: raise DGLError( f"Expect mode to be 'node', 'edge' or 'walk', got {mode}." ) self.cache = cache self.prob = None self.prefetch_ndata = prefetch_ndata or [] self.prefetch_edata = prefetch_edata or [] self.output_device = output_device def node_sampler(self, g): """Node ID sampler for random node sampler""" # Alternatively, this can be realized by uniformly sampling an edge subset, # and then take the src node of the sampled edges. However, the number of edges # is typically much larger than the number of nodes. if self.cache and self.prob is not None: prob = self.prob else: prob = g.out_degrees().float().clamp(min=1) if self.cache: self.prob = prob return ( torch.multinomial(prob, num_samples=self.budget, replacement=True) .unique() .type(g.idtype) ) def edge_sampler(self, g): """Node ID sampler for random edge sampler""" src, dst = g.edges() if self.cache and self.prob is not None: prob = self.prob else: in_deg = g.in_degrees().float().clamp(min=1) out_deg = g.out_degrees().float().clamp(min=1) # We can reduce the sample space by half if graphs are always symmetric. prob = 1.0 / in_deg[dst.long()] + 1.0 / out_deg[src.long()] prob /= prob.sum() if self.cache: self.prob = prob sampled_edges = torch.unique( choice(len(prob), size=self.budget, prob=prob) ) sampled_nodes =[src[sampled_edges], dst[sampled_edges]]) return sampled_nodes.unique().type(g.idtype) def walk_sampler(self, g): """Node ID sampler for random walk sampler""" num_roots, walk_length = self.budget sampled_roots = torch.randint(0, g.num_nodes(), (num_roots,)) traces, types = random_walk(g, nodes=sampled_roots, length=walk_length) sampled_nodes, _, _, _ = pack_traces(traces, types) return sampled_nodes.unique().type(g.idtype) def sample(self, g, indices): """Sampling function Parameters ---------- g : DGLGraph The graph to sample from. indices : Tensor Placeholder not used. Returns ------- DGLGraph The sampled subgraph. """ node_ids = self.sampler(g) sg = g.subgraph( node_ids, relabel_nodes=True, output_device=self.output_device ) set_node_lazy_features(sg, self.prefetch_ndata) set_edge_lazy_features(sg, self.prefetch_edata) return sg