spdep::listw2lines - removing duplicated lines

Hi,


I'm using spdep to generate neighbors, than listw2lines to create a
SpatialLinesDataFrame.

Considering two neighbors N1 and N2, the line will be duplicated: one
N1->N2 and one N2->N1

Only if the neighbours are symmetric, and in graph-based or k-nearest 
neighbours, this is not the case.

Would you have any idea on how to select only one line from the two, for
example the first?

If the neighbours are symmetric, it would be possible to do for example:

library(spdep)
set.seed(1)
xy <- cbind(x=runif(50), y=runif(50))
nb <- dnearneigh(xy, 0, 0.2)
nb
is.symmetric.nb(nb)
nb1 <- vector(mode="list", length=length(nb))
for (i in seq(along=nb)) nb1[[i]] <- nb[[i]][nb[[i]] <= i]
class(nb1) <- "nb"
attr(nb1, "region.id") <- attr(nb, "region.id")
nb1

It could probably also be done with gEquals() in rgeos also for asymmetric 
neighbours to remove duplications where they occur.

Roger

Actually, it would consist in removing duplicated lines with same geometry
but different directions.


Thanks in advance, any help would be greatly appreciated!

Mathieu

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Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
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