[R] kmeans cluster analysis. How do I (1) determine probability of cluster membership (2) determine cluster membership for a new subject

John Sorkin jsorkin at grecc.umaryland.edu
Tue Oct 2 17:35:12 CEST 2012

Window XP
R 2.15
I am running a cluster analysis in which I ask for three clusters (see code below). The analysis nicely tells me what cluster each of the subjects in my input dataset belongs to. I would like two pieces of information
(1) for every subject in my input data set, what is the probability of the subject belonging to each of the three cluster
(2) given a new subject, someone who was not in my original dataset, how can I determine their cluster assignment?
# K-Means Cluster Analysis
jclusters <- 3
fit       <- kmeans(datascaled, jclusters) # 3 cluster solution
and fit$cluster tells me what cluster each observation in my input dataset belongs to (output truncated for brevity):
> fit$cluster   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15  16  17 . . . .
  1   1   1   1   3   1   1   1   1   2   1   2   1   1   1   1   1 . . . . How do I get probability of being in cluster 1, cluster 2, and cluster 3 for a given subject, e.g datascaled[1,]?How do I get the cluster assigment for a new subject?Thanks,John 
John David Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology
Baltimore VA Medical Center
10 North Greene Street
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)
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