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I have calculated the kernel density of a 3-column matrix in R using the following code:

ss<-read.table("data.csv",header=TRUE,sep=",")
x<-ss[,1]
y<-ss[,2]
z<-ss[,3]
ssdata<-c(x,y,z)
ssmat<-matrix(ssdata,,3)
rp<-kde(ssmat)
plot(rp)

What I need now are the (x,y,z) coordinates of the point of maximum kernel density. Based on the answer provided at on the R-help list, I understand that the kde() function plots the joint density of the three variables in a fourth dimension which is represented in the 3d plot by shading to indicate areas of greater point density. So in effect I am trying to locate the maximum value of this "fourth" dimension. I suspect that this is a relatively simple problem but I haven't been able to find the answer. Any ideas?

missimer
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optparam
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1 Answers1

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You can extract the max value from the info returned from kde. To see all the stuff returned, use str(rp).

## Get the indices
inds <- which(abs(rp$estimate - max(rp$estimate)) < 1e-10, arr.ind=T)
xyz <- mapply(function(a, b) a[b], rp$eval.points, inds)

## Add it to plot
plot(rp)
points3d(x=xyz[1], y=xyz[2], z=xyz[3], size=20, col="blue")
Rorschach
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