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# Copyright 2001-8 by Roger Bivand
#
droplinks <- function(nb, drop, sym=TRUE) {
# class to inherits Jari Oksanen 080603
if (!inherits(nb, "nb")) stop("not a neighbours list")
n <- length(nb)
cnb <- card(nb)
if (n < 1) stop("non-positive length of nb")
if (is.logical(drop)) {
if(length(drop) != n) stop("Argument lengths differ")
idrop <- which(drop == TRUE)
} else if(is.character(drop)) {
row.names <- as.character(attr(nb, "region.id"))
idrop <- match(drop, row.names)
if(any(is.na(idrop))) stop("Region to drop not found")
} else {
idrop <- match(drop, 1:n)
if(any(is.na(idrop))) stop("Region to drop not found")
}
if((attr(nb, "sym") == FALSE) && (sym == TRUE)) {
warning("setting sym to FALSE")
sym <- FALSE
}
for (i in idrop) {
if (sym && cnb[i] > 0) {
for (j in nb[[i]])
nb[[j]] <- nb[[j]][nb[[j]] != i]
}
nb[[i]] <- 0L
}
nb <- sym.attr.nb(nb)
nb
}
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