[R] convex hull for cluster analysis

[Henrique Dallazuanna]

Try this:


plot(Y)
polygon(Y[chull(Y),])

On Tue, Nov 24, 2009 at 1:58 PM,  <james.foadi at diamond.ac.uk> wrote:
> 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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-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O