Source code for dgl.sampling.randomwalks

"""Random walk routines
"""

from .._ffi.function import _init_api
from .. import backend as F
from ..base import DGLError
from .. import ndarray as nd
from .. import utils

__all__ = [
    'random_walk',
    'pack_traces']

[docs]def random_walk(g, nodes, *, metapath=None, length=None, prob=None, restart_prob=None, return_eids=False): """Generate random walk traces from an array of starting nodes based on the given metapath. Each starting node will have one trace generated, which 1. Start from the given node and set ``t`` to 0. 2. Pick and traverse along edge type ``metapath[t]`` from the current node. 3. If no edge can be found, halt. Otherwise, increment ``t`` and go to step 2. To generate multiple traces for a single node, you can specify the same node multiple times. The returned traces all have length ``len(metapath) + 1``, where the first node is the starting node itself. If a random walk stops in advance, DGL pads the trace with -1 to have the same length. This function supports the graph on GPU and UVA sampling. Parameters ---------- g : DGLGraph The graph. nodes : Tensor Node ID tensor from which the random walk traces starts. The tensor must have the same dtype as the ID type of the graph. The tensor must be on the same device as the graph or on the GPU when the graph is pinned (UVA sampling). metapath : list[str or tuple of str], optional Metapath, specified as a list of edge types. Mutually exclusive with :attr:`length`. If omitted, DGL assumes that ``g`` only has one node & edge type. In this case, the argument ``length`` specifies the length of random walk traces. length : int, optional Length of random walks. Mutually exclusive with :attr:`metapath`. Only used when :attr:`metapath` is None. prob : str, optional The name of the edge feature tensor on the graph storing the (unnormalized) probabilities associated with each edge for choosing the next node. The feature tensor must be non-negative and the sum of the probabilities must be positive for the outbound edges of all nodes (although they don't have to sum up to one). The result will be undefined otherwise. The feature tensor must be on the same device as the graph. If omitted, DGL assumes that the neighbors are picked uniformly. restart_prob : float or Tensor, optional Probability to terminate the current trace before each transition. If a tensor is given, :attr:`restart_prob` should be on the same device as the graph or on the GPU when the graph is pinned (UVA sampling), and have the same length as :attr:`metapath` or :attr:`length`. return_eids : bool, optional If True, additionally return the edge IDs traversed. Default: False. Returns ------- traces : Tensor A 2-dimensional node ID tensor with shape ``(num_seeds, len(metapath) + 1)`` or ``(num_seeds, length + 1)`` if :attr:`metapath` is None. eids : Tensor, optional A 2-dimensional edge ID tensor with shape ``(num_seeds, len(metapath))`` or ``(num_seeds, length)`` if :attr:`metapath` is None. Only returned if :attr:`return_eids` is True. types : Tensor A 1-dimensional node type ID tensor with shape ``(len(metapath) + 1)`` or ``(length + 1)``. The type IDs match the ones in the original graph ``g``. Examples -------- The following creates a homogeneous graph: >>> g1 = dgl.graph(([0, 1, 1, 2, 3], [1, 2, 3, 0, 0])) Normal random walk: >>> dgl.sampling.random_walk(g1, [0, 1, 2, 0], length=4) (tensor([[0, 1, 2, 0, 1], [1, 3, 0, 1, 3], [2, 0, 1, 3, 0], [0, 1, 2, 0, 1]]), tensor([0, 0, 0, 0, 0])) Or returning edge IDs: >>> dgl.sampling.random_walk(g1, [0, 1, 2, 0], length=4, return_eids=True) (tensor([[0, 1, 2, 0, 1], [1, 3, 0, 1, 2], [2, 0, 1, 3, 0], [0, 1, 3, 0, 1]]), tensor([[0, 1, 3, 0], [2, 4, 0, 1], [3, 0, 2, 4], [0, 2, 4, 0]]), tensor([0, 0, 0, 0, 0])) The first tensor indicates the random walk path for each seed node. The j-th element in the second tensor indicates the node type ID of the j-th node in every path. In this case, it is returning all 0. Random walk with restart: >>> dgl.sampling.random_walk_with_restart(g1, [0, 1, 2, 0], length=4, restart_prob=0.5) (tensor([[ 0, -1, -1, -1, -1], [ 1, 3, 0, -1, -1], [ 2, -1, -1, -1, -1], [ 0, -1, -1, -1, -1]]), tensor([0, 0, 0, 0, 0])) Non-uniform random walk: >>> g1.edata['p'] = torch.FloatTensor([1, 0, 1, 1, 1]) # disallow going from 1 to 2 >>> dgl.sampling.random_walk(g1, [0, 1, 2, 0], length=4, prob='p') (tensor([[0, 1, 3, 0, 1], [1, 3, 0, 1, 3], [2, 0, 1, 3, 0], [0, 1, 3, 0, 1]]), tensor([0, 0, 0, 0, 0])) Metapath-based random walk: >>> g2 = dgl.heterograph({ ... ('user', 'follow', 'user'): ([0, 1, 1, 2, 3], [1, 2, 3, 0, 0]), ... ('user', 'view', 'item'): ([0, 0, 1, 2, 3, 3], [0, 1, 1, 2, 2, 1]), ... ('item', 'viewed-by', 'user'): ([0, 1, 1, 2, 2, 1], [0, 0, 1, 2, 3, 3]) >>> dgl.sampling.random_walk( ... g2, [0, 1, 2, 0], metapath=['follow', 'view', 'viewed-by'] * 2) (tensor([[0, 1, 1, 1, 2, 2, 3], [1, 3, 1, 1, 2, 2, 2], [2, 0, 1, 1, 3, 1, 1], [0, 1, 1, 0, 1, 1, 3]]), tensor([0, 0, 1, 0, 0, 1, 0])) Metapath-based random walk, with restarts only on items (i.e. after traversing a "view" relationship): >>> dgl.sampling.random_walk( ... g2, [0, 1, 2, 0], metapath=['follow', 'view', 'viewed-by'] * 2, ... restart_prob=torch.FloatTensor([0, 0.5, 0, 0, 0.5, 0])) (tensor([[ 0, 1, -1, -1, -1, -1, -1], [ 1, 3, 1, 0, 1, 1, 0], [ 2, 0, 1, 1, 3, 2, 2], [ 0, 1, 1, 3, 0, 0, 0]]), tensor([0, 0, 1, 0, 0, 1, 0])) """ n_etypes = len(g.canonical_etypes) n_ntypes = len(g.ntypes) if metapath is None: if n_etypes > 1 or n_ntypes > 1: raise DGLError("metapath not specified and the graph is not homogeneous.") if length is None: raise ValueError("Please specify either the metapath or the random walk length.") metapath = [0] * length else: metapath = [g.get_etype_id(etype) for etype in metapath] gidx = g._graph nodes = utils.prepare_tensor(g, nodes, 'nodes') nodes = F.to_dgl_nd(nodes) # (Xin) Since metapath array is created by us, safe to skip the check # and keep it on CPU to make max_nodes sanity check easier. metapath = F.to_dgl_nd(F.astype(F.tensor(metapath), g.idtype)) # Load the probability tensor from the edge frames ctx = utils.to_dgl_context(g.device) if prob is None: p_nd = [nd.array([], ctx=ctx) for _ in g.canonical_etypes] else: p_nd = [] for etype in g.canonical_etypes: if prob in g.edges[etype].data: prob_nd = F.to_dgl_nd(g.edges[etype].data[prob]) else: prob_nd = nd.array([], ctx=ctx) p_nd.append(prob_nd) # Actual random walk if restart_prob is None: traces, eids, types = _CAPI_DGLSamplingRandomWalk(gidx, nodes, metapath, p_nd) elif F.is_tensor(restart_prob): restart_prob = F.to_dgl_nd(restart_prob) traces, eids, types = _CAPI_DGLSamplingRandomWalkWithStepwiseRestart( gidx, nodes, metapath, p_nd, restart_prob) elif isinstance(restart_prob, float): traces, eids, types = _CAPI_DGLSamplingRandomWalkWithRestart( gidx, nodes, metapath, p_nd, restart_prob) else: raise TypeError("restart_prob should be float or Tensor.") traces = F.from_dgl_nd(traces) types = F.from_dgl_nd(types) eids = F.from_dgl_nd(eids) return (traces, eids, types) if return_eids else (traces, types)
[docs]def pack_traces(traces, types): """Pack the padded traces returned by ``random_walk()`` into a concatenated array. The padding values (-1) are removed, and the length and offset of each trace is returned along with the concatenated node ID and node type arrays. Parameters ---------- traces : Tensor A 2-dimensional node ID tensor. Must be on CPU and either ``int32`` or ``int64``. types : Tensor A 1-dimensional node type ID tensor. Must be on CPU and either ``int32`` or ``int64``. Returns ------- concat_vids : Tensor An array of all node IDs concatenated and padding values removed. concat_types : Tensor An array of node types corresponding for each node in ``concat_vids``. Has the same length as ``concat_vids``. lengths : Tensor Length of each trace in the original traces tensor. offsets : Tensor Offset of each trace in the originial traces tensor in the new concatenated tensor. Notes ----- The returned tensors are on CPU. Examples -------- >>> g2 = dgl.heterograph({ ... ('user', 'follow', 'user'): ([0, 1, 1, 2, 3], [1, 2, 3, 0, 0]), ... ('user', 'view', 'item'): ([0, 0, 1, 2, 3, 3], [0, 1, 1, 2, 2, 1]), ... ('item', 'viewed-by', 'user'): ([0, 1, 1, 2, 2, 1], [0, 0, 1, 2, 3, 3]) >>> traces, types = dgl.sampling.random_walk( ... g2, [0, 0], metapath=['follow', 'view', 'viewed-by'] * 2, ... restart_prob=torch.FloatTensor([0, 0.5, 0, 0, 0.5, 0])) >>> traces, types (tensor([[ 0, 1, -1, -1, -1, -1, -1], [ 0, 1, 1, 3, 0, 0, 0]]), tensor([0, 0, 1, 0, 0, 1, 0])) >>> concat_vids, concat_types, lengths, offsets = dgl.sampling.pack_traces(traces, types) >>> concat_vids tensor([0, 1, 0, 1, 1, 3, 0, 0, 0]) >>> concat_types tensor([0, 0, 0, 0, 1, 0, 0, 1, 0]) >>> lengths tensor([2, 7]) >>> offsets tensor([0, 2])) The first tensor ``concat_vids`` is the concatenation of all paths, i.e. flattened array of ``traces``, excluding all padding values (-1). The second tensor ``concat_types`` stands for the node type IDs of all corresponding nodes in the first tensor. The third and fourth tensor indicates the length and the offset of each path. With these tensors it is easy to obtain the i-th random walk path with: >>> vids = concat_vids.split(lengths.tolist()) >>> vtypes = concat_vtypes.split(lengths.tolist()) >>> vids[1], vtypes[1] (tensor([0, 1, 1, 3, 0, 0, 0]), tensor([0, 0, 1, 0, 0, 1, 0])) """ assert F.is_tensor(traces) and F.context(traces) == F.cpu(), "traces must be a CPU tensor" assert F.is_tensor(types) and F.context(types) == F.cpu(), "types must be a CPU tensor" traces = F.to_dgl_nd(traces) types = F.to_dgl_nd(types) concat_vids, concat_types, lengths, offsets = _CAPI_DGLSamplingPackTraces(traces, types) concat_vids = F.from_dgl_nd(concat_vids) concat_types = F.from_dgl_nd(concat_types) lengths = F.from_dgl_nd(lengths) offsets = F.from_dgl_nd(offsets) return concat_vids, concat_types, lengths, offsets
_init_api('dgl.sampling.randomwalks', __name__)