On Fri, 19 Nov 2010, Carsten Kirkeby wrote:
Hi again!
I am terribly sorry, I got a couple of wrong lines copied into the question
above. The script example should be this:
test2 <- read.gwt2nb("neighbours.txt")
summary(test2)
#and the coordinates:
coox <- c(5,5,5,5,4,3,2,1,1,2,3,4,4,3,2,1,1,2,3,4,4,3)
cooy <- c(4,3,2,1,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5)
#and a plot for illustration
plot(test2,matrix(cbind(coox,cooy),ncol=2))
text(coox,cooy,as.character(1:22),pos=rep(2,22), col="red", cex=0.8)
The .txt file is the same as above.
I think that you are assuming that nb objects assume that if i is a
neighbour of j, then j is automatically a neighbour of i. This is not the
case, and both i, j and j, i neighours must be recorded (GWT also assumes
that the user must provide all the neighbour links). In your case, try
also:
test2a <- make.sym.nb(test2)
# to make the object symmetric, assuming this was your intention
summary(test2a)
write.sn2gwt(listw2sn(nb2listw(test2a, style="B")), "neighboursA.txt")
file.show("neighboursA.txt")
to indicate what your input file perhaps should have been. I'm not sure
where you read this in ASDAR ch. 9 - it is correct that an i, j
relationship should only be given once (no duplicate directed graph
edges), but this does not mean that the presence of i, j implies that j, i
is present too (in k-nearest neighbours objects, this is very unlikely,
for example).
Hope this helps,
Roger
Sincerely
Carsten Kirkeby
--
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.biv...@nhh.no
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