differential_dataflow/algorithms/graphs/
bfs.rs

1//! Breadth-first distance labeling.
2
3use std::hash::Hash;
4
5use timely::dataflow::*;
6
7use crate::{VecCollection, ExchangeData};
8use crate::operators::*;
9use crate::lattice::Lattice;
10
11/// Returns pairs (node, dist) indicating distance of each node from a root.
12pub fn bfs<G, N>(edges: VecCollection<G, (N,N)>, roots: VecCollection<G, N>) -> VecCollection<G, (N,u32)>
13where
14    G: Scope<Timestamp: Lattice+Ord>,
15    N: ExchangeData+Hash,
16{
17    let edges = edges.arrange_by_key();
18    bfs_arranged(edges, roots)
19}
20
21use crate::trace::TraceReader;
22use crate::operators::arrange::Arranged;
23
24/// Returns pairs (node, dist) indicating distance of each node from a root.
25pub fn bfs_arranged<G, N, Tr>(edges: Arranged<G, Tr>, roots: VecCollection<G, N>) -> VecCollection<G, (N, u32)>
26where
27    G: Scope<Timestamp=Tr::Time>,
28    N: ExchangeData+Hash,
29    Tr: for<'a> TraceReader<Key<'a>=&'a N, Val<'a>=&'a N, Diff=isize>+Clone+'static,
30{
31    // initialize roots as reaching themselves at distance 0
32    let nodes = roots.map(|x| (x, 0));
33
34    // repeatedly update minimal distances each node can be reached from each root
35    nodes.clone().iterate(|scope, inner| {
36
37        let edges = edges.enter(&scope);
38        let nodes = nodes.enter(&scope);
39
40        inner.join_core(edges, |_k,l,d| Some((d.clone(), l+1)))
41             .concat(nodes)
42             .reduce(|_, s, t| t.push((*s[0].0, 1)))
43     })
44}
differential_dataflow/algorithms/graphs/bfs.rs

differential_dataflow/algorithms/graphs/
bfs.rs
