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

[Roger Bivand]

On Wed, 4 Aug 2010, Guillaume Blanchet wrote:

>
> Thanks Nikhil !!
>
> That is solving my problem !!

Maybe n.comp.nb() in spdep? This returns the number of clusters and 
cluster IDs for the observations, in your case:

> n.comp.nb(nbobj.new)
$nc
[1] 2

$comp.id
[1] 1 1 2 2 1 1 2 2

Hope this helps,

Roger


>
> Have a good day !
>
> Guillaume Blanchet
>
> Le 10-08-03 21:34, Nikhil Kaza a écrit :
>> 
>> 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
>>> 
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo at stat.math.ethz.ch
>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>> 
>> 
>
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no