[R] plot clusters
Martin Maechler
maechler at stat.math.ethz.ch
Sat Apr 26 18:43:00 CEST 2003
>>>>> "pingzhao" == pingzhao <pingzhao at waffle.cs.dal.ca>
>>>>> on Fri, 25 Apr 2003 16:45:19 -0300 writes:
pingzhao> Hi,
pingzhao> I have a dataset which has more than two clusters (say 3 clusters).
pingzhao> I used kmeans to cluster the dataset.
pingzhao> I am wondering how I can plot the clustering result on a two-dimensional
pingzhao> figure????
pingzhao> The example in the kmeans help file is as follows:
pingzhao> x <- rbind(matrix(rnorm(100, sd = 0.3), ncol = 2),
pingzhao> matrix(rnorm(100, mean = 1, sd = 0.3), ncol = 2))
pingzhao> cl <- kmeans(x, 2, 20)
pingzhao> plot(x, col = cl$cluster)
pingzhao> It seems that this is only working for 2 clusters. When my dataset has more
pingzhao> than two clusters, the plot results are obvious wrong.
Huh?!
Probably the clustering (method) wasn't what you expected,
but the plot results are obviously correct!
x3 <- rbind(matrix(rnorm(100, sd = 0.3), ncol = 2),
matrix(rnorm(100, mean = 1, sd = 0.3), ncol = 2),
matrix(rnorm(100, mean = 1.8, sd = 0.3), ncol = 2))
cl3 <- kmeans(x3, 3, 20)
plot(x3, col = cl3$cluster)
## or even more clear, and also usable on black & white :
plot(x3, col = cl3$cluster, pch = cl3$cluster)
-----
The much more interesting question is what to do when `x' has
more than two *dimensions*.
The easiest is to then plot on the first two principal
components, but I'm sure Christian Hennig will tell about much
more sophisticated solutions coming Monday...
Regards,
Martin
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