# dgl.sampling.random_walk¶

dgl.sampling.random_walk(g, nodes, *, metapath=None, length=None, prob=None, restart_prob=None)[source]

Generate random walk traces from an array of starting nodes based on the given metapath.

For a single starting node, num_traces traces would be generated. A trace would

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.

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.

Parameters
• g (DGLGraph) – The graph. Must be on CPU.

• nodes (Tensor) –

Node ID tensor from which the random walk traces starts.

The tensor must be on CPU, and must have the same dtype as the ID type of the graph.

• metapath (list[str or tuple of str], optional) –

Metapath, specified as a list of edge types.

Mutually exclusive with 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 metapath.

Only used when 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.

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, restart_prob should have the same length as metapath or length.

Returns

• traces (Tensor) – A 2-dimensional node ID tensor with shape (num_seeds, len(metapath) + 1) or (num_seeds, length + 1) if metapath is None.

• 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.

Notes

The returned tensors are on CPU.

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]))


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]))