[R-sig-Geo] error using predict.sarlm

[Roger Bivand]

On Wed, 22 Apr 2009, evans324 at umn.edu wrote:

> I am encountering difficulties using predict.sarlm to make predictions for a 
> SAR lag model generated using lagsarlm and a new dataset. I used the 
> following code to do so:
>
> dak_test.10nn.predict <- predict.sarlm(reg_vars_reduced2.10nn.lag, newdata = 
> "dak_test_data", listw = dak_test.10nn.listw, zero.policy = TRUE)

Thanks for providing the verbatim code. If this is the verbatim code, then 
newdata = "dak_test_data" is saying that newdata is not the data.frame 
object called dak_test_data, but a single element character vector - that 
is, nrow("dak_test_data") is NULL. However, this does not trigger the 
error message as such, so it could also be that you wrote newdata = 
dak_test_data, and nrow(dak_test_data) is not equal to 
length(dak_test.10nn.listw) - or here nrow(coords), which is the test.

Hope this helps,

Roger

>
> When I run this, I get the following error message: "Error in if 
> (nrow(newdata) != length(listw$neighbours)) stop("mismatch between newdata 
> and spatial weights") : argument is of length zero"
>
> I recognize that there is a problem with my listw object, but am not sure how 
> to handle it. I produced the listw using the following code sequence:
>
> dak_test.10nn <- knearneigh(coords, k=10)
> dak_test.10nn.nb <- knn2nb(dak_test.10nn, row.names=rn, sym=TRUE)
> dak_test.10nn.listw <- nb2listw(dak_test.10nn.nb, zero.policy=TRUE)
>
> Can anyone offer me some guidance in solving this problem? Thanks for your 
> help.
>
> Heather Sander
>
>
>

-- 
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