Collapsing a raster brick to a single categorical raster

raster-brick-cases.R

library(raster)
library(dplyr)

# Brick from https://gis.stackexchange.com/a/167514/65349
r1 <- raster(nrow=5, ncol=5)
b <- brick(setValues(r1, runif(ncell(r1))),
           setValues(r1, runif(25 ,0.6,0.9)),
           setValues(r1, runif(25 ,0.2,0.4)),
           setValues(r1, runif(25 ,1,2)))

# Note that each layer has a different range of values
plot(b)
hist(b)

# Example comparing raster layers to each other
# (from https://gis.stackexchange.com/a/167514/65349)
rc <- function(x1,x2,x3,x4) {
    case_when( x1 > x2 ~ 1,
               x1 < x3 ~ 2,
               TRUE ~ 0)
}

r.class <- overlay(b, fun=rc)
plot(r.class)

# Example using absolute values/thresholds/cutoffs
rc2 <- function(x1,x2,x3,x4) {
    case_when( x1 < 1 & x2 > 0.65 & x3 > .30 & x4 > 1 ~ 1, # test this case first, return class 1 if true
               x1 > 1 & x2 > 0.65 & x3 > .30 & x4 < 1 ~ 2, # test this case second, return class 2 if true
               TRUE ~ 0) # default value if no other cases match
}

r.class2 <- overlay(b, fun=rc2)
plot(r.class2)