VertexPredicateFilter.java

/*
 * Created on May 19, 2008
 *
 * Copyright (c) 2008, 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.filters;

import java.util.Collection;

import org.apache.commons.collections15.Predicate;

import edu.uci.ics.jung.graph.Graph;

/**
 * Transforms the input graph into one which contains only those vertices that
 * pass the specified <code>Predicate</code>. The filtered graph is a copy of
 * the original graph (same type, uses the same vertex and edge objects). Only
 * those edges whose entire incident vertex collection passes the predicate are
 * copied into the new graph.
 * 
 * @author Joshua O'Madadhain
 */
public class VertexPredicateFilter<V, E> implements Filter<V, E> {
	protected Predicate<V> vertex_pred;

	/**
	 * Creates an instance based on the specified vertex <code>Predicate</code>.
	 * 
	 * @param vertex_pred
	 *            the predicate that specifies which vertices to add to the
	 *            filtered graph
	 */
	public VertexPredicateFilter(Predicate<V> vertex_pred) {
		this.vertex_pred = vertex_pred;
	}

	@Override
	public Graph<V, E> transform(Graph<V, E> g) {
		Graph<V, E> filtered;
		try {
			filtered = g.newInstance();
		} catch (Exception e) {
			throw new RuntimeException(
					"Unable to create copy of existing graph: ", e);
		}

		for (V v : g.getVertices()) {
			if (vertex_pred.evaluate(v)) {
				filtered.addVertex(v);
			}
		}

		Collection<V> filtered_vertices = filtered.getVertices();

		for (E e : g.getEdges()) {
			Collection<V> incident = g.getIncidentVertices(e);
			if (filtered_vertices.containsAll(incident)) {
				filtered.addEdge(e, incident);
			}
		}

		return filtered;
	}

}