cat.to.list.R
# fields, Tools for spatial data
# Copyright 2004-2013, Institute for Mathematics Applied Geosciences
# University Corporation for Atmospheric Research
# Licensed under the GPL -- www.gpl.org/licenses/gpl.html
"cat.to.list" <- function(x, a) {
a <- as.character(a)
label <- unique(a)
out <- as.list(1:length(label))
names(out) <- label
for (k in 1:length(label)) {
out[[k]] <- x[label[k] == a]
if (length(out[[k]]) == 0)
out[[k]] <- NA
}
out
}