dpmeans {maotai}

DP-means Algorithm for Clustering Euclidean Data

Description

DP-means is a nonparametric clustering method motivated by DP mixture model in that the number of clusters is determined by a parameter \lambda. The larger the \lambda value is, the smaller the number of clusters is attained. In addition to the original paper, we added an option to randomly permute an order of updating for each observation's membership as a common heuristic in the literature of cluster analysis.

Usage

dpmeans(
  data,
  lambda = 1,
  maxiter = 1234,
  abstol = 1e-06,
  permute.order = FALSE
)

Arguments

data

an (n\times p) data matrix for each row being an observation.

lambda

a threshold to define a new cluster.

maxiter

maximum number of iterations.

abstol

stopping criterion

permute.order

a logical; TRUE if random order for permutation is used, FALSE otherwise.

Value

a named list containing

cluster

an (n\times ndim) matrix whose rows are embedded observations.

centers

a list containing information for out-of-sample prediction.

References

Kulis B, Jordan MI (2012). “Revisiting K-Means: New Algorithms via Bayesian Nonparametrics.” In Proceedings of the 29th International Coference on International Conference on Machine Learning, ICML'12, 1131–1138. ISBN 978-1-4503-1285-1.

Examples

## define data matrix of two clusters
x1  = matrix(rnorm(50*3,mean= 2), ncol=3)
x2  = matrix(rnorm(50*3,mean=-2), ncol=3)
X   = rbind(x1,x2)
lab = c(rep(1,50),rep(2,50))

## run dpmeans with several lambda values
solA <- dpmeans(X, lambda= 5)$cluster
solB <- dpmeans(X, lambda=10)$cluster
solC <- dpmeans(X, lambda=20)$cluster

## visualize the results
opar <- par(no.readonly=TRUE)
par(mfrow=c(1,4), pty="s")
plot(X,col=lab,  pch=19, cex=.8, main="True", xlab="x", ylab="y")
plot(X,col=solA, pch=19, cex=.8, main="dpmeans lbd=5", xlab="x", ylab="y")
plot(X,col=solB, pch=19, cex=.8, main="dpmeans lbd=10", xlab="x", ylab="y")
plot(X,col=solC, pch=19, cex=.8, main="dpmeans lbd=20", xlab="x", ylab="y")
par(opar)


## let's find variations by permuting orders of update
## used setting : lambda=20, we will 8 runs
sol8 <- list()
for (i in 1:8){
  sol8[[i]] = dpmeans(X, lambda=20, permute.order=TRUE)$cluster
}

## let's visualize
vpar <- par(no.readonly=TRUE)
par(mfrow=c(2,4), pty="s")
for (i in 1:8){
  pm = paste("permute no.",i,sep="")
  plot(X,col=sol8[[i]], pch=19, cex=.8, main=pm, xlab="x", ylab="y")
}
par(vpar)