[Rd] Change in the RNG implementation?

From: Hervé Pagès <hpages_at_fhcrc.org>
Date: Fri, 19 Oct 2012 16:04:12 -0700


Hi,

Looks like the implementation of random number generation changed in R-devel with respect to R-2.15.1.

ink1">With R-2.15.1:

> set.seed(33)
> sample(49821115, 10)

    [1] 22217252 19661919 24099911 45779422 42043111 25774933 21778053 17098516

    [9] 773073 5878451

With recent R-devel:

> set.seed(33)
> sample(49821115, 10)

    [1] 22217252 19661919 24099912 45779425 42043115 25774935 21778056 17098518

    [9] 773073 5878452

This is on a 64-bit Ubuntu system.

Is this change intended? I didn't see anything in the NEWS file.

A potential problem with this is that it will break unit tests for algorithms that make use of RNG.

Another more practical problem (at least for me) is the following: Bioconductor package maintainers are sometimes working hard on the development version of their package to improve the performance of some key functions. Comparing performance between BioC release (based on R-2.15) and devel (based on R-devel) often requires big input data that is randomly generated, because it's easiest than working with real data. Typically a small script is written that takes care of loading the required packages, generating the input data, and running a simple analysis. The same script is sourced in R-2.15 and R-devel, and performance and results are compared.

Not being able to generate exactly the same input in the script is a problem. It can be worked around by generating the input once, serializing it, and use load() in the script, but that makes things more complicated and the script is not a standalone script anymore (cannot be passed around without also passing around the big .rda file).

Thanks,
H.

-- 
Hervé Pagès

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024

E-mail: hpages_at_fhcrc.org
Phone:  (206) 667-5791
Fax:    (206) 667-1319

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