create nb object

Hello all,

I have a data frame with lat and lon coordinates for some sample areas (not a 
grid) .

I was to create an nb object that I can use with spdep but am unsure as to 
how to convert it.

Does anybody have any ideas?

Create a matrix of coordinates, if not using sp classes, for example:

xy <- cbind(df$x, df$y)

or if your data frame is a SpatialPointsDataFrame, just:

xy <- coordinates(obj)

Then your choice of dnearneigh(), knn2nb(knearneigh()), graph2nb() with 
three graph variants, tri2nb() for a Delaunay triangulation. The first two 
of these also take a longlat= argument in case your coordinates are 
geographical, not projected. Triangulation and graph-based methods need 
planar coordinates, so you would have to project them first.

Hope this helps,

Roger

Thanks,


Pete

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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