[Bioc-devel] reproducible with mclapply?

[Vincent Carey]

Hi, this question belongs on R-help, but perhaps

https://stat.ethz.ch/R-manual/R-devel/library/parallel/html/RngStream.html

will be useful.

Best regards

On Wed, Jun 3, 2015 at 3:11 AM, Yu, Guangchuang <gcyu at connect.hku.hk> wrote:

> Dear all,
>
> I have an issue of setting seed value when using parallel package.
>
> > library("parallel")
> > library("digest")
> >
> > set.seed(0)
> > m <- mclapply(1:10, function(x) sample(1:10),
> +               mc.cores=2)
> > digest(m, 'crc32')
> [1] "4827c80c"
> >
> > set.seed(0)
> > m <- mclapply(1:10, function(x) sample(1:10),
> +               mc.cores=2)
> > digest(m, 'crc32')
> [1] "e95b9134"
>
> By default, set.seed() will be ignored since mclapply will set the seed
> internally.
>
> If we use mc.set.seed=FALSE to disable this feature. It works as indicated
> below:
>
> > set.seed(0)
> > m <- mclapply(1:10, function(x) sample(1:10),
> +               mc.cores=2, mc.set.seed = FALSE)
> > digest(m, 'crc32')
> [1] "6bbada78"
> >
> > set.seed(0)
> > m <- mclapply(1:10, function(x) sample(1:10),
> +               mc.cores=2, mc.set.seed = FALSE)
> > digest(m, 'crc32')
> [1] "6bbada78"
>
> The problems is that the results are also depending on the number of cores.
>
> > set.seed(0)
> > m <- mclapply(1:10, function(x) sample(1:10),
> +               mc.cores=4, mc.set.seed = FALSE)
> > digest(m, 'crc32')
> [1] "a22e0aab"
>
>
> Any idea?
>
> Best Regards,
> Guangchuang
> --
> --~--~---------~--~----~------------~-------~--~----~
> Guangchuang Yu, PhD Candidate
> State Key Laboratory of Emerging Infectious Diseases
> School of Public Health
> The University of Hong Kong
> Hong Kong SAR, China
> www: http://ygc.name
> -~----------~----~----~----~------~----~------~--~---
>
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>
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