Pairwise calculations between raster layers from two different raster stacks

Question

I have 2 raster stacks. I want to do some math between pairs of raster layers from each of the stacks, producing a 3rd raster stack of the same number of layers, ie;

r1<- raster stack 1 # 10 raster layers
r2<- raster stack 2 # 10 raster layers

r3<- sqrt(r1^2 + r2^2) # 10 raster layers

Is this the equivalent of the loop form (for illustrative purposes);

for (i in 1:10) {
r <- sqrt(r1[[i]]^2 + r2[[i]]^2)
r3 <-stack(r3,r)
}

Or is there a more efficient function or apply solution? Thanks.

Yes, I think that's what I was asking. So this is the same as the loop I showed taking each pair of raster layers? I wondered if if had to unstack the raster stacks first. — user2175481

Robert Hijmans Robert Hijmans · Accepted Answer · 2018-01-30T00:57:16

Example data

library(raster)
s <- stack(system.file("external/rlogo.grd", package="raster"))

You can indeed do

x <- sqrt(s^2 + s^2)

An alternative approach would be

y <- overlay(s, s, fun=function(x, y) { sqrt(x^2 + y^2) } )

The result is the same:

all(values(x-y) == 0)
#[1] TRUE

A difference is that if you use overlay you can provide a filename to write the result to disk

Pairwise calculations between raster layers from two different raster stacks

1 Answers