Package elki.clustering.hierarchical.birch

Class CFTree

java.lang.Object

elki.clustering.hierarchical.birch.CFTree

@Reference(authors="T. Zhang, R. Ramakrishnan, M. Livny",title="BIRCH: An Efficient Data Clustering Method for Very Large Databases",booktitle="Proc. 1996 ACM SIGMOD International Conference on Management of Data",url="https://doi.org/10.1145/233269.233324",bibkey="DBLP:conf/sigmod/ZhangRL96") @Reference(authors="T. Zhang, R. Ramakrishnan, M. Livny",title="BIRCH: A New Data Clustering Algorithm and Its Applications",booktitle="Data Min. Knowl. Discovery",url="https://doi.org/10.1023/A:1009783824328",bibkey="DBLP:journals/datamine/ZhangRL97")
public class CFTree
extends java.lang.Object

Partial implementation of the CFTree as used by BIRCH.

Important differences:

1. Leaf nodes and directory nodes have the same capacity
2. Condensing and memory limits are not implemented
3. Merging refinement (merge-resplit) is not implemented

Because we want to be able to track the cluster assignments of all data points easily, we need to store the point IDs, and it is not possible to implement the originally proposed page size management at the same time.

Condensing and merging refinement are possible, and improvements to this code are welcome - please send a pull request!

References:

T. Zhang, R. Ramakrishnan, M. Livny
BIRCH: An Efficient Data Clustering Method for Very Large Databases Proc. 1996 ACM SIGMOD International Conference on Management of Data

T. Zhang, R. Ramakrishnan, M. Livny
BIRCH: A New Data Clustering Algorithm and Its Applications
Data Min. Knowl. Discovery

Since:

0.7.5

Author:

Erich Schubert

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	CFTree.Factory	CF-Tree Factory.
static class	CFTree.LeafIterator	Iterator over leaf nodes.

Field Summary

Fields

Modifier and Type	Field	Description
(package private) BIRCHAbsorptionCriterion	absorption	Criterion for absorbing points.
(package private) int	capacity	Capacity of a node.
(package private) BIRCHDistance	distance	Distance function to use.
(package private) int	leaves	Leaf node counter.
static Logging	LOG	Class logger.
(package private) CFTree.TreeNode	root	Current root node.
(package private) double	thresholdsq	Squared maximum radius threshold of a clustering feature.

Constructor Summary

Constructors

Constructor	Description
CFTree(BIRCHDistance distance, BIRCHAbsorptionCriterion absorption, double threshold, int capacity)	Constructor.

Method Summary

Modifier and Type	Method	Description
private boolean	add(ClusteringFeature[] children, ClusteringFeature child)	Add a node to the first unused slot.
private double	estimateThreshold(CFTree.TreeNode current)
private ClusteringFeature	findLeaf(CFTree.TreeNode node, NumberVector nv)	Find the leaf of a cluster, to get the final cluster assignment.
ClusteringFeature	findLeaf(NumberVector nv)	Find the leaf of a cluster, to get the final cluster assignment.
private CFTree.TreeNode	insert(CFTree.TreeNode node, ClusteringFeature nleaf)	Recursive insertion.
private CFTree.TreeNode	insert(CFTree.TreeNode node, NumberVector nv)	Recursive insertion.
void	insert(NumberVector nv)	Insert a data point into the tree.
CFTree.LeafIterator	leafIterator()	Get an iterator over the leaf nodes.
protected java.lang.StringBuilder	printDebug(java.lang.StringBuilder buf, ClusteringFeature n, int d)	Utility function for debugging.
protected void	rebuildTree()	Rebuild the CFTree to condense it to approximately half the size.
private CFTree.TreeNode	split(CFTree.TreeNode node, ClusteringFeature newchild)	Split an overfull node.

Methods inherited from class java.lang.Object

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

Field Detail

LOG

public static final Logging LOG

Class logger.

distance

BIRCHDistance distance

Distance function to use.

absorption

BIRCHAbsorptionCriterion absorption

Criterion for absorbing points.

thresholdsq

double thresholdsq

Squared maximum radius threshold of a clustering feature.

capacity

int capacity

Capacity of a node.

root

CFTree.TreeNode root

Current root node.

leaves

int leaves

Leaf node counter.

Constructor Detail

CFTree

public CFTree(BIRCHDistance distance,
              BIRCHAbsorptionCriterion absorption,
              double threshold,
              int capacity)

Constructor.

Parameters:

distance - Distance function to use

absorption - Absorption criterion

threshold - Threshold

capacity - Capacity

Method Detail

insert

public void insert(NumberVector nv)

Insert a data point into the tree.

Parameters:

nv - Object data

rebuildTree

protected void rebuildTree()

Rebuild the CFTree to condense it to approximately half the size.

estimateThreshold

private double estimateThreshold(CFTree.TreeNode current)

insert

private CFTree.TreeNode insert(CFTree.TreeNode node,
                               NumberVector nv)

Recursive insertion.

Parameters:

node - Current node

nv - Object data

Returns:

New sibling, if the node was split.

findLeaf

public ClusteringFeature findLeaf(NumberVector nv)

Find the leaf of a cluster, to get the final cluster assignment.

In contrast to insert(elki.data.NumberVector), this does not modify the tree.

Parameters:

nv - Object data

Returns:

Leaf this vector should be assigned to

findLeaf

private ClusteringFeature findLeaf(CFTree.TreeNode node,
                                   NumberVector nv)

Find the leaf of a cluster, to get the final cluster assignment.

In contrast to insert(elki.data.NumberVector), this does not modify the tree.

TODO: allow "outliers"?

Parameters:

node - Current node

nv - Object data

Returns:

Leaf this vector should be assigned to

split

private CFTree.TreeNode split(CFTree.TreeNode node,
                              ClusteringFeature newchild)

Split an overfull node.

Parameters:

node - Node to split

newchild - Additional child

Returns:

New sibling of node

insert

private CFTree.TreeNode insert(CFTree.TreeNode node,
                               ClusteringFeature nleaf)

Recursive insertion.

Parameters:

node - Current node

nleaf - Leaf entry to add.

Returns:

New sibling, if the node was split.

add

private boolean add(ClusteringFeature[] children,
                    ClusteringFeature child)

Add a node to the first unused slot.

Parameters:

children - Children list

child - Child to add

Returns:

false if node is full

leafIterator

public CFTree.LeafIterator leafIterator()

Get an iterator over the leaf nodes.

Returns:

Leaf node iterator.

printDebug

protected java.lang.StringBuilder printDebug(java.lang.StringBuilder buf,
                                             ClusteringFeature n,
                                             int d)

Utility function for debugging.

Parameters:

buf - Output buffer

n - Current node

d - Depth

Returns:

Output buffer