Applying different equation based on conditional statement for raster value in R?

Question

I am trying to find the best way to apply a set of equations to a raster conditional on values in a separate raster. For example, suppose r1 has the values of interest and raster 2 (r2) is a raster with three values, 1, 2, and 3.

r1 <- raster(nrow=5, ncol=5)
r1[] <- runif(ncell(r1)) * 10
r2 = raster(nrow=5,ncol=5)
r2[] = round(runif(ncell(r2),1,3))
r3 = 0/r2 ## holder for values

I have modified code that applies a conditional function and applies it to a matrix, then assigns the values of the matrix to the raster.

Con=function(condition, trueValue, falseValue){
 return(condition * trueValue + (!condition)*falseValue)}

fun1 = function(x){x*1}
fun2 = function(x){x*2}
fun3 = function(x){x*3}
m = as.matrix(Con(r2 == 1,fun1(r1),Con(r2 == 2, fun2(r1), Con(r2 == 3,fun3(r1),0))))
values(r3) = m

This works, but (a) the conditional statement is highly unreadable, and (b) I am concerned that is will be prone to error with larger rasters.

Does anyone have a better way of doing this?

Answer 1

You could approach it this way:

f <- function(x,y) {
    z <- rep(NA, length(x))
    i <- which(y == 1)
    z[i] <- x[i] * 3
    i <- which(y == 2)
    z[i] <- x[i] * 33
    i <- which(y == 3)
    z[i] <- x[i] * 333
    z
}

library(raster)
r1 <- r2 <- raster(nrow=5, ncol=5)
r1[] <- runif(ncell(r1)) * 10
r2[] <- round(runif(ncell(r2),1,3))

x <- overlay(r1, r2, fun=f)