将图划分为具有相同 class 的邻居组

Question

Using JGraphT , I would like partition a graph into groups where each group consists of a connected sub-graph of vertices that have the same "class" (denoted using colors below).

Example -- the desired groups are in red:

I think this is a rather simple demand and yet I can't find a (built-in) way to do this. I notice there is a PartitioningImpl class, that one constructs using a List<Set<V>> classes , yet I don't see a way to use this to partition a graph.

Ideally, I'd provide something with my graph and vertex classes (a map of V --> Integer for instance) and it would return something like a List<Set<V>> of partitioned vertex groups.

Answer 1

Sometimes you just cannot avoid writing some code

LOOP over classes
   LOOP over nodes that are in class
       Copy node to new graph
   LOOP over edges that connect nodes in class
       Copy edge to new graph
   LOOP over connected components in new graph
       Save component as a group graph for class

Answer 2

This is a fairly simple approach using JGraphT:

First remove edges linking neighbouring vertices that belong to different classes and then use ConnectivityInspector on the reduced graph to find connected components , which form the groups.

SimpleGraph<V, E> graph; // given by user
Map<V, Integer> classes; // given by user

List<E> toRemove = new ArrayList<>();
graph.edgeSet().forEach(e -> {
    V a = graph.getEdgeSource(e);
    V b = graph.getEdgeTarget(e);
    if (!classes.get(a).equals(classes.get(b))) {
        toRemove.add(e);
    }
});

graph.removeAllEdges(toRemove);
ConnectivityInspector<V, E> ci = new ConnectivityInspector<>(graph);
List<Set<V>> groups = ci.connectedSets();