Package org.jgrapht.traverse

Class RandomWalkIterator<V,E>

java.lang.Object

org.jgrapht.traverse.AbstractGraphIterator<V,E>

org.jgrapht.traverse.RandomWalkIterator<V,E>

Type Parameters:

V - vertex type

E - edge type

All Implemented Interfaces:

java.util.Iterator<V>, GraphIterator<V,E>

public class RandomWalkIterator<V,E>
extends AbstractGraphIterator<V,E>

A random walk iterator for a directed or undirected graph.

At each step the iterator selects a random (uniformly distributed) edge out of the current vertex and follows it to the next vertex. In case of directed graphs the outgoing edge set is used. See wikipedia for more details.

In case a weighted walk is desired, edges are selected with probability respective to its weight (out of the total weight of the edges). The walk can be bounded by number of steps (default Long#MAX_VALUE . When the bound is reached the iterator is considered exhausted. Calling next() on exhausted iterator will throw NoSuchElementException. In case a sink (i.e. no edges) vertex is reached, any consecutive calls to next() will throw NoSuchElementException.

For this iterator to work correctly the graph must not be modified during iteration. Currently there are no means to ensure that, nor to fail-fast. The results of such modifications are undefined.

Author:

Assaf Mizrachi

Field Summary

Fields inherited from class org.jgrapht.traverse.AbstractGraphIterator

crossComponentTraversal, graph, nListeners, reusableEdgeEvent, reusableVertexEvent, reuseEvents

Constructor Summary

Constructors

Constructor	Description
RandomWalkIterator(Graph<V,E> graph)	Creates a new iterator for the specified graph.
RandomWalkIterator(Graph<V,E> graph, V startVertex)	Creates a new iterator for the specified graph.
RandomWalkIterator(Graph<V,E> graph, V startVertex, boolean isWeighted)	Creates a new iterator for the specified graph.
RandomWalkIterator(Graph<V,E> graph, V startVertex, boolean isWeighted, long maxSteps)	Creates a new iterator for the specified graph.
RandomWalkIterator(Graph<V,E> graph, V startVertex, boolean isWeighted, long maxSteps, java.util.Random rng)	Creates a new iterator for the specified graph.

Method Summary

Modifier and Type	Method	Description
protected void	encounterVertex(V vertex, E edge)	Update data structures every time we see a vertex.
boolean	hasNext()
protected boolean	isExhausted()	Check if this walk is exhausted.
V	next()

Methods inherited from class org.jgrapht.traverse.AbstractGraphIterator

addTraversalListener, createEdgeTraversalEvent, createVertexTraversalEvent, fireConnectedComponentFinished, fireConnectedComponentStarted, fireEdgeTraversed, fireVertexFinished, fireVertexTraversed, getGraph, isCrossComponentTraversal, isReuseEvents, remove, removeTraversalListener, setCrossComponentTraversal, setReuseEvents

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Iterator

forEachRemaining

Constructor Detail

RandomWalkIterator

public RandomWalkIterator(Graph<V,E> graph)

Creates a new iterator for the specified graph. Iteration will start at arbitrary vertex. Walk is un-weighted and bounded by Long#MAX_VALUE steps.

Parameters:

graph - the graph to be iterated.

Throws:

java.lang.IllegalArgumentException - if graph==null or does not contain startVertex

RandomWalkIterator

public RandomWalkIterator(Graph<V,E> graph,
                          V startVertex)

Creates a new iterator for the specified graph. Iteration will start at the specified start vertex. If the specified start vertex is null, Iteration will start at an arbitrary graph vertex. Walk is un-weighted and bounded by Long#MAX_VALUE steps.

Parameters:

graph - the graph to be iterated.

startVertex - the vertex iteration to be started.

Throws:

java.lang.IllegalArgumentException - if graph==null or does not contain startVertex

RandomWalkIterator

public RandomWalkIterator(Graph<V,E> graph,
                          V startVertex,
                          boolean isWeighted)

Creates a new iterator for the specified graph. Iteration will start at the specified start vertex. If the specified start vertex is null, Iteration will start at an arbitrary graph vertex. Walk is bounded by Long#MAX_VALUE steps.

Parameters:

graph - the graph to be iterated.

startVertex - the vertex iteration to be started.

isWeighted - set to true if a weighted walk is desired.

Throws:

java.lang.IllegalArgumentException - if graph==null or does not contain startVertex

RandomWalkIterator

public RandomWalkIterator(Graph<V,E> graph,
                          V startVertex,
                          boolean isWeighted,
                          long maxSteps)

Creates a new iterator for the specified graph. Iteration will start at the specified start vertex. If the specified start vertex is null, Iteration will start at an arbitrary graph vertex. Walk is bounded by the provided number steps.

Parameters:

graph - the graph to be iterated.

startVertex - the vertex iteration to be started.

isWeighted - set to true if a weighted walk is desired.

maxSteps - number of steps before walk is exhausted.

Throws:

java.lang.IllegalArgumentException - if graph==null or does not contain startVertex

RandomWalkIterator

public RandomWalkIterator(Graph<V,E> graph,
                          V startVertex,
                          boolean isWeighted,
                          long maxSteps,
                          java.util.Random rng)

Creates a new iterator for the specified graph. Iteration will start at the specified start vertex. If the specified start vertex is null, Iteration will start at an arbitrary graph vertex. Walk is bounded by the provided number steps.

Parameters:

graph - the graph to be iterated.

startVertex - the vertex iteration to be started.

isWeighted - set to true if a weighted walk is desired.

maxSteps - number of steps before walk is exhausted.

rng - the random number generator to use

Throws:

java.lang.IllegalArgumentException - if graph==null or does not contain startVertex

Method Detail

isExhausted

protected boolean isExhausted()

Check if this walk is exhausted. Calling next() on exhausted iterator will throw NoSuchElementException.

Returns:

trueif this iterator is exhausted, false otherwise.

encounterVertex

protected void encounterVertex(V vertex,
                               E edge)

Update data structures every time we see a vertex.

Parameters:

vertex - the vertex encountered

edge - the edge via which the vertex was encountered, or null if the vertex is a starting point

hasNext

public boolean hasNext()

next

public V next()