[R-sig-Geo] From contiguity matrices to neighbours lists

[Roger Bivand]

On Tue, 25 May 2004, Millo Giovanni wrote:

> Dear all,
> 
> Having previously constructed by hand a (plain vanilla) contiguity
> matrix among n regions, i.e. nxn with x_ij=1 if i and j are neighbours,
> 0 otherwise, we wondered if there is some convenient function for
> transforming this into a neighbours list in order to carry on an
> analysis in spdep. 

mat2listw(<your matrix>)$neighbours should do it.

> 
> Else, if we are forced to do this by hand, it would be good to have a
> precise spec sheet of "how an nb object should look like"... We didn't
> find that in the spdep manual, maybe because it is easier than we think
> :^).
> 
I'll add this to the documentation TODO - are vignettes or regular help 
files preferable?


> Third way: we have a map of the regions of interest (Italy, NUTS3) in
> the maps package, maybe there is some conversion tool towards "nb"?
> 

This will be happening, as of now in relation to the "sp" package on 
sourceforge, but it hasn't happened yet. Keeping the region names 
associated with the polygons is essential, and knowing when to use 
multi-polygons (how many polygons make up a region) too, so there is 
plenty to do -- help welcome!

Roger

> Thank you for your help
> 
> Giovanni Millo
> R&D Dept.
> Assicurazioni Generali SpA
> Trieste, Italy
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no