On 12-10-19 7:04 PM, Hervé Pagès wrote:
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.
I think it was mentioned in the NEWS:
\code{sample.int()} has some support for \eqn{n \ge
2^{31}}{n >= 2^31}: see its help for the limitations.
A different algorithm is used for \code{(n, size, replace = FALSE,
prob = NULL)} for \code{n > 1e7} and \code{size <= n/2}. This
is much faster and uses less memory, but does give different results.
I don't think the old algorithm is available, but perhaps it could be
made available by an optional parameter.
Duncan Murdoch
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