problem with 'islands' in neighbourhood matrix

I created a neighbourhood matrix in GeoDa and have read it into R using 
read.gal (spdep package).  I have a few zero-neighbour polygons and as a 
result I cannot apply nb2listw to my nb object.  Is there a way to get 
around this problem when reading in the .gal file or do these islands 
need to be removed before creating the matrix?

Functions in spdep use an argument called zero.policy=, set by default to 
FALSE, which stop you using neighbour or weights lists with zero-neighbour 
entities. You override this by saying zero.policy=TRUE.

An alternative is to subset your data and the neighbour list:

have_neighbours <- card(nb) > 0
sub_nb <- subset(nb, have_neighbours)
sub_data <- subset(data, have_neighbours)

So the problem can be handled internally. Finally, if you want to stitch 
them onto the graph of neighbours, have a look at ?edit.nb (you'll need 
the centroids of the polygons for this).

Thanks,
Meredith Franklin

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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.Bivand at nhh.no