stream (version 1.0-3)

DSC_Reachability: Reachability Micro-Cluster Reclusterer

Description

Implementation of reachability clustering (based on DBSCAN's concept of reachability) to recluster a set of micro-clusters. Two micro-clusters are directly reachable if they are within each other's epsilon-neighborhood (i.e., the distance between the centers is less then epsilon). Two micro-clusters are reachable if they are connected by a chain of pairwise directly reachable micro-clusters. All mutually reachable micro-clusters are put in the same cluster.

Usage

DSC_Reachability(epsilon, min_weight=NULL, description=NULL)

Arguments

epsilon

radius of the epsilon-neighborhood.

min_weight

micro-clusters with a weight less than this will be ignored for reclustering.

description

optional character string to describe the clustering method.

Value

• An object of class DSC_Reachability. The object contains the following items:
• description
  The name of the algorithm in the DSC object.
• RObj
  The underlying R object.

Details

Reachability uses internally DSC_Hierarchical with single link.

Note that this clustering cannot be updated iteratively and every time it is used for (re)clustering, the old clustering is deleted.

References

Martin Ester, Hans-Peter Kriegel, Joerg Sander, Xiaowei Xu (1996). A density-based algorithm for discovering clusters in large spatial databases with noise. In Evangelos Simoudis, Jiawei Han, Usama M. Fayyad. Proceedings of the Second International Conference on Knowledge Discovery and Data Mining (KDD-96). AAAI Press. pp. 226-231.

See Also

DSC, DSC_Macro

Examples

dsd <- DSD_mlbenchGenerator("cassini")

# Recluster micro-clusters from tNN with reachability using epsilon=2r, i.e.,
# two micro-clusters are reachable if their assignment areas overlap.
tnn <- DSC_tNN(r=0.1)
cluster(tnn, dsd, 500)

reach <- DSC_Reachability(epsilon=0.2)
recluster(reach, tnn)
  
plot(reach, dsd, type="both")  

# For comparison we using reachability clustering directly on data points
# Note: reachability is not a data stream clustering algorithm!
reach <- DSC_Reachability(epsilon=0.2)
cluster(reach, dsd, 500)
reach
plot(reach, dsd)