Error in simulation R-code

First I apologize all of you for annoying messages. Since I did not receive
the mail I sent, I thought there might be some errors.

On Wed, Jul 15, 2009 at 5:13 PM, Roger Bivand <Roger.Bivand at nhh.no> wrote:

On Wed, 15 Jul 2009, Steve Hong wrote:

 Dear List,

I have a question about simulation code. Here are the code and error
message.

 sim.sp <- function(data,CM,n,N)

+ {
+   C <- matrix(rep(NA,N),ncol=1)
+ for(i in 1:N)
+ {
+ j <- n
+ xx <- which(colSums(CM[j,])==1)
+ V <- names(xx)
+ V <- paste(V, collapse="+")
+ V <- paste("SBA~", V)
+ rd <- round(nrow(data)*(2/3))
+ d <- sample(seq(1:nrow(data)),rd)
+ dat1 <- data[d,]
+ dat2 <- data[-d,]
+ crd <- cbind(dat1$Longitude,dat1$Latitude)
+ dist80 <- dnearneigh(crd,0,100,longlat=F)
+ dist80sw <- nb2listw(dist80, style="B")
+ fm <- errorsarlm(as.formula(V), data=dat1, listw=dist60sw)
+ pred <- predict(fm,dat2)
+ C[i,1] <- cor(dat2$SBA,pred)
+ out <- cbind(C)
+ }
+ colMeans(out)
+ }

sim.sp(df2007.5k.s2,CM,1,1000)

Error in nb2listw(dist80, style = "B") : Empty neighbour sets found

I guess it means that there are some observations without neighborhoods
from
random selection process. Is there any way to proceed simulation like
using
only ones with neighborhood sets?

Any suggestion will be appreciated!!

This is the fourth separate posting of this message, in addition
cross-posted to R-help. Please do consider the bandwidth costs and the
negative consequences of cross-posting. If you can't wait for someone else
to use their time to solve your (simple) problem, perhaps a little
reflection is called for?

Have you read ?dnearneigh and ?nb2listw? The examples in ?dnearneigh show
how to use the maximum 1st nearest neighbour distances to set the d2=
argument to a value ensuring that each observation has at least one
neighbour. Given your use of Longitude and Latitude as coordinate names, are
you sure that longlat= should be FALSE, or are the names simply careless?
This could affect what you think 100 units is - if coordinates in m, it is
100m, if in US surveyors feet, then 100ft, if degrees, 100 degrees ... which
affects the d2= value. dist80 looks an odd name for d2=100 as well, doesn't
it? You check for zero neighbour counts by:

Dist80, Longitude, and Latitude are careless. Please ignore that. Actually,
Longitude and Latitude are UTM values (In that case longlat=F, right?). I
think '100' is 100 km. It was OK when I try to get predicted value without
simulation.

any(card(nb) == 0)

In ?nb2listw, you find the zero.policy= argument, which has a default value
of FALSE, but which you can set to TRUE, so avoiding the error in your
simulation if used consistently in subsequent function calls to functions
taking that argument, like errorsarlm(). So:

zp <- !any(card(nb) == 0)
..., zero.policy=zp, ...

Where should I add these codes? Can I add the first code (zp <-!...) in
front of nb2listw? The second one should be in nb2listw(....,
zero.policy=zp). Is that correct?

might be OK, unless you also need to check that there are any neighbours at
all.

I'm not at all sure that this simulation is going to get you anywhere
sensible - why are you trying to do it? I do hope you are setting the seed
before running it, otherwise you won't know what is going wrong in the
situations you choose. You are posting from a gmail address, and so not give
any affiliation in your signature. Is this a homework problem?

Fortunately, this is NOT a homework problem. I am post-graduated. I changed
my email address to a gamil address from the work address (educational
institute). I did that since I wanted to separate R-related emails from my
work email address. I am in the lists of R-help, R-sig-geo, R-mixed, and
R-ecology.

Again, you only took 40 minutes in sending 4 copies of the same message to
two lists. Replying has taken about the same time. Reading two help pages
would have taken you much less.

Again, I sincerely apologize for sending same messages. It is totally my
misstake. I thought it did not get there since I could not see it in my
gmail account. If I use gmail address, can't I see that?

Thank you!!

Roger Bivand

Thank you!

Steve Hong

       [[alternative HTML version deleted]]

--
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