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@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]]
>>
>> _______________________________________________
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>> R-sig-Geo@stat.math.ethz.ch
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>>
> --
> 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@nhh.no
>
>

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