[Bioc-devel] reproducible with mclapply?

The only bad thing I see so far in using set.seed inside the function is
that it interferes with previously set seed by the user.  So follow-up
stochastic computation will be out user's control.  Perhaps there are other
undesirable effect that I do not see at this point.
I tweaked the solution a bit here that wraps mclapply/lapply and maintains
the user control of stochasticity by resetting the seed to some random
value generated based on users input.

http://stackoverflow.com/questions/30610375/how-to-run-permutations-using-mclapply-in-a-reproducible-way-regardless-of-numbe/30627984#30627984
I tend to agree though that in a long run doRNG is the way to go.

On Thu, Jun 4, 2015 at 8:15 AM, Valerie Obenchain <vobencha at fredhutch.org>
wrote:

I'll add a section to the BiocParallel docs.

Valerie

On 06/04/2015 07:55 AM, Kasper Daniel Hansen wrote:

Yes, based on the documentation that particular random stream generator
would work with mclapply.

This is absolutely a subject which ought to be covered in the
BiocParallel
documentation.

And commenting on another set of recommendations: please NEVER used
set.seed inside a function.  Unfortunately, because of the way R works,
this is a really bad idea.  As is functions with arguments like
(set.seed =
FALSE).  Users need to be educated about this.  The main issue with using
set.seed is when your work is wrapped into other peoples code, for
example
with an external bootstrap or similar.  I understand the desire for
reproducibility, but the design of the random generator in R is such that
this should really be left to the user.

Kasper

On Thu, Jun 4, 2015 at 10:39 AM, Vincent Carey <
stvjc at channing.harvard.edu>

wrote:

 It does appear to me that the doRNG vignette sec 1.1 describes a

solution
to the problem posed.  It is less clear to me that this method is
readily
adopted with BiocParallel unless registerDoPar is in use....  Should we
address this topic explicitly in the vignette?

On Thu, Jun 4, 2015 at 9:50 AM, Kasper Daniel Hansen <
kasperdanielhansen at gmail.com> wrote:

 Note you're not guaranteed that two random streams starting with

different
seeds will be (approximately) independent, so the suggestion on SO
makes
the numbers reproducible but technically wrong.

If you want true independence you either need to use a parallel
version of
the random number generator or you do what I suggested.  Because of how
mclapply works (via fork) it is not clear to me that it is possible to
use
a parallel version of the random number generator, but I am not sure
about
this.  The snippet from the documentation quoted above suggests I am
wrong.

Best,
Kasper

On Wed, Jun 3, 2015 at 11:25 PM, Vladislav Petyuk <petyuk at gmail.com>
wrote:

 There are different ways set.seed can be used.  The way it is

suggested

on

the aforementioned stackoverflow post is basically a two stage
process.
First seed is provided by a user (set.seed(1)).  That is user can
change
the outcome from run to run.  Based on that seed, a vector of
randomized
seeds is generated (seeds <- sample.int(length(input),
replace=TRUE)).
Those seeds are basically arguments to the function under

mclapply/lapply

that help to control random number generation for each iteration

(set.seed

(seeds[idx])).
There are two different roles of set.seed. First left the user to

control

random number generation and the second (within the function) makes
sure
that it is the same for individual iterations regardless how the loop
is
executed.
Does that make sense?

On Wed, Jun 3, 2015 at 7:07 PM, Yu, Guangchuang <gcyu at connect.hku.hk>
wrote:

 There is one possible solution posted in

http://stackoverflow.com/questions/30610375/how-to-run-permutations-using-mclapply-in-a-reproducible-way-regardless-of-numbe/30627984#30627984

.

As Kasper suggested, it's not a proper way to use set.seed inside a
package.

I suggest using a parameter for example seed=FALSE to disable the

set.seed

and if user want the result reproducible, e.g. in demonstration, set

seed=TRUE explicitly and set.seed will be run inside the function.

Bests,
Guangchuang

On Wed, Jun 3, 2015 at 8:42 PM, Kasper Daniel Hansen <
kasperdanielhansen at gmail.com> wrote:

 For this situation, generate the permutation indexes outside of the

mclapply, and the do mclapply over a list with the indices.

And btw., please don't use set.seed inside a package; that control

should

completely be left to the user.

Best,
Kasper

On Wed, Jun 3, 2015 at 7:08 AM, Vincent Carey <

stvjc at channing.harvard.edu>

wrote:

 This document indicates how to achieve reproducibility independent

of

the

underlying physical environment.

http://cran.r-project.org/web/packages/doRNG/vignettes/doRNG.pdf

Let me know if that satisfies the question.

On Wed, Jun 3, 2015 at 5:32 AM, Yu, Guangchuang <

gcyu at connect.hku.hk>

wrote:

 Der Vincent,

RNGkind("L'Ecuyer-CMRG") works as using mc.set.seed=FALSE.

When mc.cores changes, the output is not reproducible.

I think this issue is also of concern within the Bioconductor

community

as parallel version of permutation test is commonly used now.

Best Regards,

Guangchuang



On Wed, Jun 3, 2015 at 5:17 PM, Vincent Carey <

stvjc at channing.harvard.edu>

wrote:

 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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--
--~--~---------~--~----~------------~-------~--~----~
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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         [[alternative HTML version deleted]]

--
--~--~---------~--~----~------------~-------~--~----~
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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