On Mon, 11 Oct 2010, Dennis Guignet wrote:
Dear All,
My end goal is to run a spatial lag model, where the weight matrix will
be nonsymmetric and contain observations with zero neighbors. I am
having some difficulties in creating the neighbor list in R. Any advice
or pointers on where to find more information would be greatly
appreciated.
Maybe try some other format, such as the MATLAB-style sparse matrix in
read.dat2listw(). However then you cannot use your codes, just the
sequence 1:n. If this doesn't help, put the file(s) on a website and post
the link - debugging without the input data is hard. I can't follow how a
region with only zero links has non-zero links (below).
Roger
I needed to account for both time and space when defining a list of
neighbors, and did so first using ArcInfo and then SAS, and saved the
final list as a dbf. It seems I next want to convert this dbf into a
neighbor list in R, and was told the best thing to do is save the dbf as
a gwt file and change the header line. A brief portion is pasted below:
0 34451 nfred3 DGID
105450 105578 1
105451 105763 1
105451 105627 1
105451 105899 1
105451 105898 1
105451 105915 1
105452 105763 1
105452 105841 1
nfred3 is the name of the gwt file, and DGID is the unique id for each
observation. There are a total of 34,451 unique observations, some of
which do not have any neighbors and are thus not included in the above
gwt file. If I run gwt2nb accounting for these zero link observations I
get the following warning messages:
DGID<-sales$dgid
length(DGID)
[1] 34451
n2n<-read.gwt2nb("nfred3.gwt", region.id=DGID)
Warning messages:
1: In read.gwt2nb("nfred3.gwt", region.id = DGID) :
region.id not named DGID
2: In read.gwt2nb("nfred3.gwt", region.id = DGID) :
105462, 105463, 105466, 105468, 105472, ... [... truncated]
3: In read.gwt2nb("nfred3.gwt", region.id = DGID) :
105450, 105454, 105455, 105462, 105468, ... [... truncated]
The issue is that there are a total of 1,555 regions with no links, but
1,090 of these regions should have a positive number of links . The
truncated list in the warning message contains id numbers that should
have zero links, as well as some that should have nonzero links.
If I run similar code but only account for observations with nonzero
links, then I have the correct number of nonzero links. So this neighbor
list at first glance seems correct, but I still need to account for
observations with zero links when later forming the weights, and I am
concerned about the below warning messages.
#create vector of unique sale ids with nonzero spatial link (i.e. has neighbors)
n2n0<-read.table("nfred4.gwt",header=FALSE,skip=1)
DGID<-unique(n2n0$V1)
length(DGID)
[1] 33986
n2n<-read.gwt2nb("nfred4.gwt", region.id=DGID)
Warning messages:
1: In read.gwt2nb("nfred4.gwt", region.id = DGID) :
region.id not named DGID
2: In read.gwt2nb("nfred4.gwt", region.id = DGID) :
105450, 105454, 105455, 105470, ... [... truncated]
Any advice or pointers of where I can find some helpful info would be
greatly appreciated.
Thank you,
Denny
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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.biv...@nhh.no
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