[R] R extract vertices for polygon

[David Winsemius]

On Jul 21, 2009, at 10:18 PM, Angel Marley wrote:

>
> Dear R users,
> I'm trying to extract from a given matrix (GROUP) the coordinates of  
> the vertices of the different groups (i.e. 3, 7, 1 . . .) to plot  
> the polygons to delineate the area in which each group "wins" and  
> colour it diferentially. I can make a simple point plot, but I would  
> like to add polygons with full colored area. The example is with a  
> 5x5 matrix, but I'm working with 500 x 500 matrix, so hand work is  
> difficult,
> Any suggestion will be welcomed.
>
> Nrep=5
> GROUP<- 
> matrix(c(3,3,3,3,7,3,3,3,3,7,1,3,3,3,7,1,3,3,3,7,1,1,4,4,0),Nrep,Nrep)
> column<- seq(1, 5, length=Nrep)
> row<- seq(0,10,length=Nrep)
>
> colnames(GROUP)<- round(column,3)
> rownames(GROUP)<- row
>
> GROUP
>
> grupovec<-as.vector(GROUP)
> flushvec<-rep(column,rep(Nrep,Nrep))
> MORvec<-rep(row,Nrep)
>
> plot(flushvec,MORvec, col=grupovec, pch=19)
>
> polygon() # ????????????????????????????????????
>
> Thanks
> Angel

I am having trouble figuring out what variables represents  
coordinates, but that's probably my problem and it's clear in your  
head. There are several convex hull functions that you can find with:

<http://search.r-project.org/cgi-bin/namazu.cgi?query=convex+hull&max=100&result=normal&sort=score&idxname=functions&idxname=Rhelp08&idxname=views 
 >

Or if the wrapping breaks that URL just:

http://search.r-project.org/

-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT