[R] convex hull for cluster analysis

[james.foadi at diamond.ac.uk]

Dear R gurus and users,
I seem to have problem finding the right tool for plotting convex hulls over
2D plots, after a cluster analysis. In fact I would like to draw a convex hull
in 2D for a generic group of points. I found a "convhulln", but this doesn't seem
to give me a convex hull. Here is what I do:


> library(mvtnorm)
> Mean <- c(2,1)
> Sigma <- matrix(c(1,0,0,1),ncol=2)
> Y <- rmvnorm(n=100,mean=Mean,sigma=Sigma)
> hull <- convhulln(Y)
> hull
      [,1] [,2]
 [1,]   16   26
 [2,]   16    4
 [3,]   87   47
 [4,]   87    4
 [5,]   21   26
 [6,]   21   94
 [7,]   54   47
 [8,]   54   75
 [9,]   23   94
[10,]   23   75


I was expecting hull to give me a few 2D points that would enclose the 100 random points generated,
but this doen't seem to be the case.

Probably I'm using the wrong tool here.
Any help with this would be greatly appreciated. Thank you.

J

Dr James Foadi PhD
Membrane Protein Laboratory (MPL)
Diamond Light Source Ltd
Diamond House
Harewell Science and Innovation Campus
Chilton, Didcot
Oxfordshire OX11 0DE

Email    :  james.foadi at diamond.ac.uk
Alt Email:  j.foadi at imperial.ac.uk


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