mclapply() doesn’t work, as it should, on Windows. Therefore, Nathan VanHoudnos has published a package called parallelsugar which replaces mclapply() with a mclapply() that actually works on Windows. You can read more about it here: r-bloggers.com/parallelsugar-an-implementation-of-mclapply-for-windows/ To avoid masking parallelsugar‘s mclapply with parallel‘s mclapply you can use: parallelsugar::mclapply().