Re: [R-sig-Geo] Complete neighbours

[Roger Bivand]

On Fri, 3 Sep 2010, German Sanchez Hernandez wrote:

Dear list,

I would like to complete my neighbour list in order to increase the 
number of neighbours of regions with less neighbours (links) than a 
certain number. The idea is to complete these links using knearneigh 
function.


My try:

nb <- poly2nb(map)
# Compute distribution of linkage:
distr <- as.data.frame(table(card(nb)))
# Try to identify the "isolated" regions (equal or less than, for example, 3 
neighbours
minim <- 3 # It's a computed number
isolated <- subset(nb, subset=card(nb) <= minim)
# Get the "isolated" region IDs
regions <- attr(unclass(isolated), 'region.id')
# Modify nb using knearneigh ¿?

For the edited version of nblag_cumul on R-forge on the spdep project, 
you'd do something like:

example(columbus)
table(card(col.gal.nb))
k4 <- knn2nb(knearneigh(coordinates(columbus), 4))
mod_nb <- nblag_cumul(list(col.gal.nb, k4))
table(card(mod_nb))

but I'm not at all sure that this is a good idea. Most often observations 
with few neighbours are on the edge of the data set, so there is a very 
good reason for their apparent "isolation".

Hope this helps,

Roger



# Alternative 2:
nbmat <- nb2mat(nb)
# Modify nbmat ¿?, mat2listw, listw2nb


# Alternative 3:
listw <- nb2listw(nb)
# Modify listw ¿?, listw2nb


The question is:

How to modify nb (or nbmat or listw) to increase the number of links of 
the "isolated" regions?

Any idea?

Thank you!
Germán Sánchez
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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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