[R] parallel computing with foreach()

[Peter Langfelder]

Your code generates an error that has nothing to do with dopar. I have
no idea what your function stack is supposed to do; you may be
inadvertently calling utils::stack which would produce this kind of
error:

> stack(1:25, RAT = FALSE)
Error in data.frame(values = unlist(unname(x)), ind, stringsAsFactors = FALSE) :
  arguments imply differing number of rows: 25, 0

HTH,

Peter

On Wed, Dec 6, 2017 at 10:03 PM, Kumar Mainali <kpmainali at gmail.com> wrote:
> I have used foreach() for parallel computing but in the current problem, it
> is not working. Given the volume and type of the data involved in the
> analysis, I will try to give below the complete code without reproducible
> example.
>
> In short, each R environment will draw a set of separate files, perform the
> analysis and dump in separate folders.
>
> splist <- c("juoc", "juos", "jusc", "pico", "pifl", "pipo", "pire", "psme")
> covset <- c("PEN", "Thorn")
>
> foreach(i = 1:length(splist)) %:%
> foreach(j = 1:length(covset)) %dopar% {
>
> spname <- splist[i]; spname
> myTorP <- covset[j]; myTorP
>
> DataSpecies = data.frame(prsabs = rep(1, 10), lon = rep(30, 10), lat =
> rep(80, 10))
> myResp = as.numeric(DataSpecies[,1])
> myRespXY = DataSpecies[, c("lon", "lat")]
> # directory of a bunch of raster files specific to each R environment
> rastdir <- paste0(rootdir, "Current/", myTorP); rastdir
> rasterc = list.files(rastdir, pattern="\\.tif$", full.names = T)
> print(rasterc)
> myExplc = stack(rasterc, RAT=FALSE)
> }
>
> I get the following error message that most likely generates while stacking
> rasters because there are 25 rasters in the folder of each environment.
> Also, in the normal for loop, this reads all fine.
> Error in { :
>   task 1 failed - "arguments imply differing number of rows: 25, 0"
>
> Thank you.
> ᐧ
>
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>
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