From hpages at fhcrc.org  Sat Oct 20 01:04:12 2012
From: hpages at fhcrc.org (=?ISO-8859-1?Q?Herv=E9_Pag=E8s?=)
Date: Fri, 19 Oct 2012 16:04:12 -0700
Subject: [Rd] Change in the RNG implementation?
Message-ID: <5081DC6C.2010306@fhcrc.org>

Hi,

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

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.

-- 
Herv? Pag?s

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
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[Rd] Change in the RNG implementation?
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