[R-sig-Geo] classify a raster by unique value

Robert Hijmans r.hijmans at gmail.com
Fri Jul 15 16:22:25 CEST 2011

>> I've a raster stack with 3 layers. 
>> I need to classify it assigning one class to each unique combination of
>> values. 

> Perhaps the below works. It may be very slow if unq has many rows. 

That was not quite right, I think it works when you do:

unq <- unique(as.matrix(data_stack)) 

fun  <- function(x, ...) { 
        r <- rep(NA, nrow(x)) 
        for (i in 1:nrow(unq)) { 
                r[ which(apply(t(x) == unq[i,], 2, sum) == ncol(unq)) ] <- i 

x  <- calc(data_stack, fun) 

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