[R-sig-Geo] Automatically count independent group of points

[Nikhil Kaza]

This may be a overkill. but no.clusters in igraph package might work.

require(igraph)
nbobj <- cell2nb(4,2,"rook")
nb.mat <- nb2mat(nbobj)
no.clusters(graph.adjacency(nb.mat))


Nikhil Kaza
Asst. Professor,
City and Regional Planning
University of North Carolina

nikhil.list at gmail.com

On Aug 3, 2010, at 4:57 PM, Guillaume Blanchet wrote:

> Hi !
>
> I am currently working on a wombling (boundary detection) function  
> and I have come across a nag. Hopefully you will be able to give me  
> a hand on this.
>
> Following is a small example to explain what I want to do using the  
> spdep package.
>
> xy<-expand.grid(1:4,1:2)
> nbobj<-cell2nb(4,2,"rook")
>
> links<-listw2sn(nb2listw(nbobj))
> links.new<-links[-c(4,6,15,17),]
>
> nbobj.new<-sn2listw(links.new)$neighbours
>
> plot(nbobj.new,xy)
>
> "nbobj.new" has two separate groups of points links between each  
> other. Is there a way to automatically counts the number of  
> independent (non-linked) groups of sites ?
>
> Thanks in advance !
>
> Guillaume Blanchet
>
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