[Rd] Change in the RNG implementation?

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


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).


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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Received on Fri 19 Oct 2012 - 23:08:58 GMT

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