How to perform operations between raster stacks and repeat the operations to all the folders in R?

I am a new user of R. My questions is closed to a recent asked questions on stack overflow website:How to stack individual raster layers from files contained in individual subfolders in R? . I used the answers provided for my own case. I have several folders containing several raster files. The description of the files is the same for each folder. To simplify, I have two folders A and B containing each 16 rasters files. Either folder A or B, raster files have the same type of name so they can be identified with patterns.

                        |----8 raster files pattern "snow"
              Folder A- |      
              |         |----8 raster files pattern "rain"
parent_folder-|
              |        |----8 raster files pattern "snow"
              Folder B-|      
                       |----8 raster files pattern "rain"

I used the code provided in the last question (see link):

list_dirs <- list.dirs("path/parentfolder/", recursive = F)

names(list_dirs) <- basename(list_dirs)


# create two stacks with the pattern "snow" for the folders A and B, respectively

raster.list.snow <- lapply(list_dirs, function(dir) {
stack(list.files(dir, pattern = "snow", full.names = T, recursive = F))
})

# create two stacks with the pattern "rain" for the folders A and B, respectively

raster.list.rain <- lapply(list_dirs, function(dir) {
stack(list.files(dir, pattern = "rain", full.names = T, recursive = F))
})

I would like to perform calculis within each folder. For example, I would like in the folder A to multiply raster stack with the pattern "snow" with the raster stack with the pattern '"rain", and that doing the same thing for the folder B.

I tried the following code:

   raster.multiply<- raster.list.snow * raster.list.rain

I should have 8 new raster files for each folder A and B.

Then I would like to write in each folder the files obtained from raster.multiply.

However, for the last line of code, I got the following error:

 Error in raster.list.snow * raster.list.rain : 
 non-numeric argument to binary operator

I am very new in R and I am still exploring.

Solution

yuo wont be able to multiply the resulting lists of rasters together like that, hence the error (go investigate lists).

but you can easily stack lists of stacks:

# make some dummy rasters
a <- raster(xmn=0,xmx=5,ymn=0,ymx=5,res=1)
a[] <- sample(1:5,25,replace=T)
b <- raster(xmn=0,xmx=5,ymn=0,ymx=5,res=1)
b[] <- sample(1:5,25,replace=T)
c <- raster(xmn=0,xmx=5,ymn=0,ymx=5,res=1)
c[] <- sample(1:5,25,replace=T)
d <- raster(xmn=0,xmx=5,ymn=0,ymx=5,res=1)
d[] <- sample(1:5,25,replace=T)

# imagine st1 and st2 are rain rasters, st3 and st4 are snow
st1 <- stack(a,b,c,d)
st2 <- stack(d,a,c,b)
st3 <- stack(c,b,a,d)
st4 <- stack(a,d,b,c)

# make the rain and snow lists, just like your code above. we have a list object of two stacks.
list1 <- list(st1,st2)
list2 <- list(st3,st4)

# error below
list1 * list2
Error in list1 * list2 : non-numeric argument to binary operator

# however, stack them and multiply:
stack(list1) * stack(list2)

# check e.g.
identical(getValues(stack(list1)[[1]]),getValues(a))
[1] TRUE