[R-sig-Geo] creating an adjacency matrix in spdep

[Stratford, Jeffrey]

Thanks Roger,  I did read through I just wanted to make sure. When I
read "nearest neighbor" I think of the point closest to another point
and I think I am looking for a matrix of distances between all points -
so the two ideas (nearest neighbor and adjacency matrix) didn't jive in
my head.  Do I have it right though - is the adjacency matrix a
rectangular matrix of distances (or inverse distances) between points? I
was able to run the functions you mentioned but I don't get the matrix
I'm looking for.  Here's what I have so far:

# creating and exporting an adjacency matrix
library(spdep)
sosp09 <- read.csv("g:\\sosp\\2009\\sosp2009c.csv", header=T)
n <- nrow(sosp09)
plot(sosp09$x, sosp09$y)
coords <-cbind(sosp09$x, sosp09$y)
coordinates(sosp09) <- c("x","y")
# these are the USGS coordinates
distan <- dnearneigh(coords, 0, 100000)
distan2 <- make.sym.nb(distan)
plot(distan, coords)

# When I pull up distan and distan2 I get a summary 

Neighbour list object:
Number of regions: 53 
Number of nonzero links: 2740 
Percentage nonzero weights: 97.54361 
Average number of links: 51.69811

Thanks the help!  I'm going through your spatial book and it's really
good - lots of tips! 

-----Original Message-----
From: Roger Bivand [mailto:Roger.Bivand at nhh.no] 
Sent: Monday, January 31, 2011 3:30 AM
To: Stratford, Jeffrey
Cc: r-sig-geo at r-project.org
Subject: Re: [R-sig-Geo] creating an adjacency matrix in spdep

On Sun, 30 Jan 2011, Stratford, Jeffrey wrote:

> Hi everyone,
>
>
>
> Is it possible to create an adjacency matrix required for
> WinBUGS/GeoBUGS in spdep from a csv file containing UTM coordinates?
>
>
>
> I've gone through the spdep documentation and it looks like the
> equivalent there is col.gal.nb?  Is that right?  I see where that
object
> is used but not how it was created.
>

There is plenty of documentation in spdep on the creation of nb objects
if 
you look for it. For point support (your case), you can choose between 
dnearneigh() for distance-based neighbours, knn2nb(knearneigh()) for k 
nearest neighbours (will need making summetric with make.sym.nb() for 
WinBUGS), or the various graph2nb() variants (which may also need making

symmetric). The case you refer to from ?nb2WB refers to ?columbus, which

explains that col.gal.nb is an nb object imported from an original 
GAL-format file for compatibility with GeoDa - the example shows how, 
using read.gal(). You should also be able to read the *.gal or *.gwt
files 
you made in GeoDa with read.gal() or read.gwt2nb(), then out again with 
nb2WB().

Hope this helps,

Roger

>
>
> I also realize that I can get the same through GeoDa but I haven't
been
> able to figure out how to export the adj matrix from there.
>
>
>
> Many thanks,
>
>
>
> Jeff
>
>
>
> *****************************************
>
> Jeffrey A. Stratford, Ph.D.
>
> Department of Health and Biological Sciences
>
> 84 W. South St.
>
> Wilkes Univertsity, PA 18766
>
> 570-332-2942
>
> http://web.wilkes.edu/jeffrey.stratford/
>
> *****************************************
>
>
>
>
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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