/*
* Copyright (c) 2003, the JUNG Project and the Regents of the University
* of California
* All rights reserved.
*
* This software is open-source under the BSD license; see either
* "license.txt" or
* http://jung.sourceforge.net/license.txt for a description.
*/
package edu.uci.ics.jung.algorithms.transformation;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import org.apache.commons.collections15.Factory;
import org.apache.commons.collections15.Transformer;
import org.apache.commons.collections15.functors.MapTransformer;
import edu.uci.ics.jung.algorithms.blockmodel.VertexPartition;
import edu.uci.ics.jung.graph.Graph;
/**
* This class transforms a graph with a known vertex partitioning into a graph
* whose vertices correspond to the input graph's partitions. Two vertices in
* the output graph are connected if and only if there exists at least one edge
* between vertices in the corresponding partitions of the input graph. If the
* output graph permits parallel edges, there will be an edge connecting two
* vertices in the new graph for each such edge connecting constituent vertices
* in the input graph.
*
* <p>
* Concept based on Danyel Fisher's <code>GraphCollapser</code> in JUNG 1.x.
*
*/
public class VertexPartitionCollapser<V, E, CV, CE> {
protected Factory<Graph<CV, CE>> graph_factory;
protected Factory<CV> vertex_factory;
protected Factory<CE> edge_factory;
protected Map<Set<V>, CV> set_collapsedv;
/**
* Creates an instance with the specified graph and element factories.
*
* @param vertex_factory
* used to construct the vertices of the new graph
* @param edge_factory
* used to construct the edges of the new graph
* @param graph_factory
* used to construct the new graph
*/
public VertexPartitionCollapser(Factory<Graph<CV, CE>> graph_factory,
Factory<CV> vertex_factory, Factory<CE> edge_factory) {
this.graph_factory = graph_factory;
this.vertex_factory = vertex_factory;
this.edge_factory = edge_factory;
this.set_collapsedv = new HashMap<Set<V>, CV>();
}
/**
* Creates a new graph whose vertices correspond to the partitions of the
* supplied graph.
*
* @param partitioning
* @return a new graph whose vertices correspond to the partitions of the
* supplied graph
*/
public Graph<CV, CE> collapseVertexPartitions(
VertexPartition<V, E> partitioning) {
Graph<V, E> original = partitioning.getGraph();
Graph<CV, CE> collapsed = graph_factory.create();
// create vertices in new graph corresponding to equivalence sets in the
// original graph
for (Set<V> set : partitioning.getVertexPartitions()) {
CV cv = vertex_factory.create();
collapsed.addVertex(vertex_factory.create());
set_collapsedv.put(set, cv);
}
// create edges in new graph corresponding to edges in original graph
for (E e : original.getEdges()) {
Collection<V> incident = original.getIncidentVertices(e);
Collection<CV> collapsed_vertices = new HashSet<CV>();
Map<V, Set<V>> vertex_partitions = partitioning
.getVertexToPartitionMap();
// collect the collapsed vertices corresponding to the original
// incident vertices
for (V v : incident) {
collapsed_vertices
.add(set_collapsedv.get(vertex_partitions.get(v)));
}
// if there's only one collapsed vertex, continue (no edges to
// create)
if (collapsed_vertices.size() > 1) {
CE ce = edge_factory.create();
collapsed.addEdge(ce, collapsed_vertices);
}
}
return collapsed;
}
/**
* Returns a transformer from vertex sets in the original graph to collapsed
* vertices in the transformed graph.
*/
public Transformer<Set<V>, CV> getSetToCollapsedVertexTransformer() {
return MapTransformer.getInstance(set_collapsedv);
}
}