Clustering Categorical Data Pasi Fränti 18.2.2016
K-means clustering
Definitions and data Set of N data points: Partition of the data: X={x1, x2, …, xN} Partition of the data: P={p1, p2, …, pM}, Set of M cluster prototypes (centroids): C={c1, c2, …, cM},
Distance and cost function Euclidean distance of data vectors: Mean square error:
Clustering result as partition Partition of data Cluster prototypes Illustrated by Voronoi diagram Illustrated by Convex hulls
Duality of partition and centroids Partition of data Cluster prototypes Partition by nearest prototype mapping Centroids as prototypes
Categorical data
Categorical clustering Three attributes director actor genre t1 (Godfather II) Coppola De Niro Crime t2 (Good Fellas) Scorsese t3 (Vertigo) Hitchcock Stewart Thriller t4 (N by NW) Grant t5 (Bishop's Wife) Koster Comedy t6 (Harvey)
Categorical clustering Sample 2-d data: color and shape Model A Model B Model C
Hamming Distance (Binary and categorical data) Number of different attribute values. Distance of (1011101) and (1001001) is 2. Distance (2143896) and (2233796) Distance between (toned) and (roses) is 3. 100->011 has distance 3 (red path) 010->111 has distance 2 (blue path) 3-bit binary cube
Histogram-based methods: K-means variants Methods: Histogram-based methods: k-modes k-medoids k-distributions k-histograms k-populations k-representatives
Entropy-based cost functions Category utility: Entropy of data set: Entropies of the clusters relative to the data:
Iterative algorithms
K-modes clustering Distance function
K-modes clustering Prototype of cluster
K-medoids clustering Prototype of cluster Vector with minimal total distance to every other 3 Medoid: 2 2 A C E B C F B D G B C F 2+3=5 2+2=4 2+3=5
K-medoids Example
K-medoids Calculation
K-histograms D 2/3 F 1/3
K-distributions Cost function with ε addition
Example of cluster allocation Change of entropy
Problem of non-convergence Non-convergence
Results with Census dataset
Literature Modified k-modes + k-histograms: M. Ng, M.J. Li, J. Z. Huang and Z. He, On the Impact of Dissimilarity Measure in k-Modes Clustering Algorithm, IEEE Trans. on Pattern Analysis and Machine Intelligence, 29 (3), 503-507, March, 2007. ACE: K. Chen and L. Liu, The “Best k'' for entropy-based categorical dataclustering, Int. Conf. on Scientific and Statistical Database Management (SSDBM'2005), pp. 253-262, Berkeley, USA, 2005. ROCK: S. Guha, R. Rastogi and K. Shim, “Rock: A robust clustering algorithm for categorical attributes”, Information Systems, Vol. 25, No. 5, pp. 345-366, 200x. K-medoids: L. Kaufman and P. J. Rousseeuw, Finding groups in data: an introduction to cluster analysis, John Wiley Sons, New York, 1990. K-modes: Z. Huang, Extensions to k-means algorithm for clustering large data sets with categorical values, Data mining knowledge discovery, Vol. 2, No. 3, pp. 283-304, 1998. K-distributions: Z. Cai, D. Wang and L. Jiang, K-Distributions: A New Algorithm for Clustering Categorical Data, Int. Conf. on Intelligent Computing (ICIC 2007), pp. 436-443, Qingdao, China, 2007. K-histograms: Zengyou He, Xiaofei Xu, Shengchun Deng and Bin Dong, K-Histograms: An Efficient Clustering Algorithm for Categorical Dataset, CoRR, abs/cs/0509033, http://arxiv.org/abs/cs/0509033, 2005.