org.graphstream.algorithm
Class ConnectedComponents

java.lang.Object
  org.graphstream.stream.SinkAdapter
      org.graphstream.algorithm.ConnectedComponents

All Implemented Interfaces:

Algorithm, DynamicAlgorithm, org.graphstream.stream.AttributeSink, org.graphstream.stream.ElementSink, org.graphstream.stream.Sink

public class ConnectedComponents
extends org.graphstream.stream.SinkAdapter
implements DynamicAlgorithm

Compute and update the number of connected components of a dynamic graph.

This algorithm computes the connected components for a given graph. Connected components are the set of its connected subgraphs. Two nodes belong to the same connected component when there exists a path (without considering the direction of the edges) between them. Therefore, the algorithm does not consider the direction of the edges. The number of connected components of an undirected graph is equal to the number of connected components of the same directed graph. See wikipedia for details.

Dynamics

This algorithm tries to handle the dynamics of the graph, trying not to recompute all from scratch at each change (kind of re-optimization). In this way, each instance of the algorithm is registered as a graph sink. Each change in the graph topology may affect the algorithm.

Usage

To start using the algorithm, you first need an instance of Graph, then you only have to instantiate the algorithm class. Whether you specify a reference to the graph in the constructor or you set it with the init(Graph) method.

The computation of the algorithm starts only when the graph is specified with the init(Graph) method or with the appropriated constructor. In case of a static graph, you may call the compute() method. In case of a dynamic graph, the algorithm will compute itself automatically when an event (node or edge added or removed) occurs.

Finally you may ask the algorithm for the number of connected components at any moment with a call to the getConnectedComponentsCount() method.

Example

 import org.graphstream.algorithm.ConnectedComponents;
 import org.graphstream.graph.Graph;
 import org.graphstream.graph.implementations.DefaultGraph;
 
 public class CCTest {
        public static void main(String[] args) {
 
                Graph graph = new DefaultGraph("CC Test");
 
                graph.addNode("A");
                graph.addNode("B");
                graph.addNode("C");
                graph.addEdge("AB", "A", "B");
                graph.addEdge("AC", "A", "C");
 
                ConnectedComponents cc = new ConnectedComponents();
                cc.init(graph);
 
                System.out.printf("%d connected component(s) in this graph, so far.%n",
                                cc.getConnectedComponentsCount());
 
                graph.removeEdge("AC");
 
                System.out.printf("Eventually, there are %d.%n",
                                cc.getConnectedComponentsCount());
 
        }
 }
 

Additional features

Threshold and Ceiling

It is possible to get rid of connected components belong a size threshold when counting the overall number of connected components. It is also possible to define a ceiling size for the connected component. Above that size ceiling, connected components will not be counted. Use the getConnectedComponentsCount(int) or getConnectedComponentsCount(int, int) methods.

Components Identifiers

You can tag each node with an integer that identifies the component it pertains to using setCountAttribute(String). The argument of this method is an arbitrary name that will be used as attribute on each node of the graph. The value of this attribute will be an integer (counting from zero) that is different for each connected component.

Giant component

The getGiantComponent() method gives you a list of nodes belonging to the biggest connected component of the graph.

Cut Attribute

The cut attribute is a feature that can optionally simulate a given edge to be invisible (as if the edge did not exist). In other words if an edge is given such a cut attribute, it will be ignored by the algorithm when counting. You can enable (or disable by passing null) the cut attribute by specifying it with the setCutAttribute(String) method, and by giving the special edges the same attribute.

What is it useful for? Well you may want to simulate the removal of a given edge and see if it increases the number of connected components. You may not want to really remove and then re-add that edge in the graph, because such removal event may have consequences on other algorithms, viewer, writers...

Note that setting the cut attribute will trigger a new computation of the algorithm.

Since:

June 26 2007

Author:

Yoann Pigné, Antoine Dutot, Guillaume-Jean Herbiet

Computational Complexity :

For the initial computation, let n be the number of nodes, then the complexity is 0(n). For the re-optimization steps, let k be the number of nodes concerned by the changes (k <= n), the complexity is O(k).

Constructor Summary

ConnectedComponents()
Construction of an instance with no parameter.

ConnectedComponents(org.graphstream.graph.Graph graph)
Constructor with the given graph.

Method Summary

void	compute() Run the algorithm.
void	edgeAdded(String graphId, long timeId, String edgeId, String fromNodeId, String toNodeId, boolean directed)
void	edgeAttributeAdded(String graphId, long timeId, String edgeId, String attribute, Object value)
void	edgeAttributeRemoved(String graphId, long timeId, String edgeId, String attribute)
void	edgeRemoved(String graphId, long timeId, String edgeId)
int	getConnectedComponentsCount() Ask the algorithm for the number of connected components.
int	getConnectedComponentsCount(int sizeThreshold) Ask the algorithm for the number of connected components whose size is equal to or greater than the specified threshold.
int	getConnectedComponentsCount(int sizeThreshold, int sizeCeiling) Ask the algorithm for the number of connected components whose size is equal to or greater than the specified threshold and lesser than the specified ceiling.
List<org.graphstream.graph.Node>	getGiantComponent() Computes a list of nodes that belong to the biggest connected component.
void	graphCleared(String graphId, long timeId)
void	init(org.graphstream.graph.Graph graph) Initialization of the algorithm.
void	nodeAdded(String graphId, long timeId, String nodeId)
void	nodeRemoved(String graphId, long timeId, String nodeId)
void	setCountAttribute(String countAttribute) Enable (or disable by passing null for countAttribute) an optional attribute that will be assigned to each node.
void	setCutAttribute(String cutAttribute) Enable (or disable by passing null) an optional attribute that makes edges that have it invisible (as if the edge did not existed).
void	terminate() Terminate the dynamic algorithm.

Methods inherited from class org.graphstream.stream.SinkAdapter

edgeAttributeChanged, graphAttributeAdded, graphAttributeChanged, graphAttributeRemoved, nodeAttributeAdded, nodeAttributeChanged, nodeAttributeRemoved, stepBegins

Methods inherited from class java.lang.Object

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

Constructor Detail

ConnectedComponents

public ConnectedComponents()

Construction of an instance with no parameter. The process is not initialized and the algorithm will not receive any event from any graph. You will have to call the init(Graph) method with a reference to a graph so that the computation is able to start. After the init(Graph) method is invoked, the computation starts as soon as and event is received or if the compute() method is invoked.

ConnectedComponents

public ConnectedComponents(org.graphstream.graph.Graph graph)

Constructor with the given graph. The computation of the algorithm start only when the init(Graph) method is invoked. This Constructor will call the init(Graph) method anyway.

Parameters:

graph - The graph who's connected components will be computed.

Method Detail

getGiantComponent

public List<org.graphstream.graph.Node> getGiantComponent()

Computes a list of nodes that belong to the biggest connected component.

Returns:

nodes of the biggest CC.

getConnectedComponentsCount

public int getConnectedComponentsCount()

Ask the algorithm for the number of connected components.

Returns:

the number of connected components in this graph.

getConnectedComponentsCount

public int getConnectedComponentsCount(int sizeThreshold)

Ask the algorithm for the number of connected components whose size is equal to or greater than the specified threshold.

Parameters:

sizeThreshold - Minimum size for the connected component to be considered

Returns:

the number of connected components, bigger than the given size threshold, in this graph.

getConnectedComponentsCount

public int getConnectedComponentsCount(int sizeThreshold,
                                       int sizeCeiling)

Ask the algorithm for the number of connected components whose size is equal to or greater than the specified threshold and lesser than the specified ceiling.

Parameters:

sizeThreshold - Minimum size for the connected component to be considered

sizeCeiling - Maximum size for the connected component to be considered (use 0 or lower values to ignore the ceiling)

Returns:

the number of connected components, bigger than the given size threshold, and smaller than the given size ceiling, in this graph.

setCutAttribute

public void setCutAttribute(String cutAttribute)

Enable (or disable by passing null) an optional attribute that makes edges that have it invisible (as if the edge did not existed). Be careful, setting the cut attribute will trigger a new computation of the algorithm.

Parameters:

cutAttribute - The name for the cut attribute or null if the cut attribute option must be disabled.

setCountAttribute

public void setCountAttribute(String countAttribute)

Enable (or disable by passing null for countAttribute) an optional attribute that will be assigned to each node. The value of this attribute will be an integer different for each computed component.

Parameters:

countAttribute - The name of the attribute to put on each node (pass null to disable this feature).

init

public void init(org.graphstream.graph.Graph graph)

Description copied from interface: Algorithm

Initialization of the algorithm. This method has to be called before the Algorithm.compute() method to initialize or reset the algorithm according to the new given graph.

Specified by:

init in interface Algorithm

Parameters:

graph - The graph this algorithm is using.

compute

public void compute()

Description copied from interface: Algorithm

Run the algorithm. The Algorithm.init(Graph) method has to be called before computing.

Specified by:

compute in interface Algorithm

See Also:

Algorithm.init(Graph)

terminate

public void terminate()

Description copied from interface: DynamicAlgorithm

Terminate the dynamic algorithm.

Specified by:

terminate in interface DynamicAlgorithm

See Also:

Algorithm.init(org.graphstream.graph.Graph)

edgeAdded

public void edgeAdded(String graphId,
                      long timeId,
                      String edgeId,
                      String fromNodeId,
                      String toNodeId,
                      boolean directed)

Specified by:

edgeAdded in interface org.graphstream.stream.ElementSink

Overrides:

edgeAdded in class org.graphstream.stream.SinkAdapter

nodeAdded

public void nodeAdded(String graphId,
                      long timeId,
                      String nodeId)

Specified by:

nodeAdded in interface org.graphstream.stream.ElementSink

Overrides:

nodeAdded in class org.graphstream.stream.SinkAdapter

edgeRemoved

public void edgeRemoved(String graphId,
                        long timeId,
                        String edgeId)

Specified by:

edgeRemoved in interface org.graphstream.stream.ElementSink

Overrides:

edgeRemoved in class org.graphstream.stream.SinkAdapter

nodeRemoved

public void nodeRemoved(String graphId,
                        long timeId,
                        String nodeId)

Specified by:

nodeRemoved in interface org.graphstream.stream.ElementSink

Overrides:

nodeRemoved in class org.graphstream.stream.SinkAdapter

graphCleared

public void graphCleared(String graphId,
                         long timeId)

Specified by:

graphCleared in interface org.graphstream.stream.ElementSink

Overrides:

graphCleared in class org.graphstream.stream.SinkAdapter

edgeAttributeAdded

public void edgeAttributeAdded(String graphId,
                               long timeId,
                               String edgeId,
                               String attribute,
                               Object value)

Specified by:

edgeAttributeAdded in interface org.graphstream.stream.AttributeSink

Overrides:

edgeAttributeAdded in class org.graphstream.stream.SinkAdapter

edgeAttributeRemoved

public void edgeAttributeRemoved(String graphId,
                                 long timeId,
                                 String edgeId,
                                 String attribute)

Specified by:

edgeAttributeRemoved in interface org.graphstream.stream.AttributeSink

Overrides:

edgeAttributeRemoved in class org.graphstream.stream.SinkAdapter