Multiplication of two raster stack with R using multicore parallel processes

Question

I am working with two global raster stacks, each containing 60 layers using the R Software. The layers are global raster files (in GTiff format) at a resolution of 5 min of arc. The first stack contains cultivated areas for 60 crops, while the second stack contains the grid-cell yield of the same 60 crops.

my objective is to multiply the two raster stacks, in order to obtain the production for the 60 crops for each grid-cell. I am running this calculation using the raster package and using its parallelizing function clusterR together with the fuction calc. I am running the process using 24 cores. The code looks like this:

rasters_production <- clusterR(rasters_land_use_hectars, calc, args=list(fun=function(x){x*rasters_yield}),
                        export="rasters_yield", exclude="parallel", filename=paste0("Script_generated_files/", "organic_rasters_production_1.tif"), format="GTiff", overwrite=T, cl=cluster)

When I run it, the code generate the following error:

Error in clusterR(rasters_land_use_hectars, calc, args = list(fun = function(x) { : cluster error

Nevertheless, if I run the same multiplication but multiplying a raster stack for a vector of 60 coefficient (and not for a second raster stack), the calculation works correctly?

Does somebody know why the calculation between the two raster stacks does not work instead?

Answer 1

if you look at the documentation for ClusterR you'll see you need a couple extra lines of code, like:

beginCluster(cpus = n)
x <- clusterR(stuff)
endCluster()

you may also need forceapply = TRUE in your calc function, unless I'm misreading what you're trying to do.

Answer 2

You can also use mclapply in parallel package, where NUM_CORES is the total number of cores you wanna use.

 rasters_production <- stack(mclapply(1:nlayers(rasters_yield)), function(i){ 
        rasters_land_use_hectars[[i]] * rasters_yield[[i]]
    }, mc.cores = NUM_CORES))