On 03/05/2020 3:43 p.m., Fomby, Tom wrote:
Dear Duncan,
OK, I will certainly ask my students to download the most recent version
of Basic R at the first of each semester and, just to be safe, include
the RNGkind(sample.kind="Rejection") command before the students get
started on the data partitioning part of their exercise using the sample
function.
Actually, it would probably be a better idea to say
RNGkind(kind = "default", normal.kind = "default", sample.kind = "default")
in case bugs are found in any of the current algorithms and they change
again.
By the way, how is it that one can take a membership in the R community
so as to provide support for volunteers like yourself.
The R Foundation accepts donations to become a "Supporting Member"; see
here: https://www.r-project.org/foundation/donors.html. They sponsor
various events, so that is one way. There is probably also a local user
group somewhere near you that would appreciate contributions of some
sort. There's a list of those here:
https://blog.revolutionanalytics.com/local-r-groups.html, and another
one here: https://www.meetup.com/pro/r-user-groups/. (I haven't
checked how similar those two lists are.)
Duncan Murdoch
Thank you,
Tom Fomby
Department of Economics
SMU
Dallas, TX 75275
------------------------------------------------------------------------
*From:* Duncan Murdoch <murdoch.dun...@gmail.com>
*Sent:* Sunday, May 3, 2020 2:32 PM
*To:* Fomby, Tom; r-help@R-project.org
*Subject:* Re: [R] Question about "sample" function and inconsistent
results I am getting across machines.
On 03/05/2020 1:39 a.m., Fomby, Tom wrote:
Please consider the following code:
set.seed(1)
train.index = sample(181,150)
head(train.index)
# [1] 49 67 103 162 36 159 Result from my ASUS computer
#
# [1] 68 167 129 162 43 14 Result from my wife's HP Pavilion computer
In both cases, version 3.6.3 of R are being used.
In addition, of the 20 students in my Predictive Analytics class, 14 got the first result while 6 got the latter result. These results do not seem to be specific to MAC (OS) versus PC (Windows). In several cases, students using 3.6.3 got differing results. This makes grading of homework challenging not knowing which partitions
of the data are being used by the student.
Thank you for considering my question.
Likely some of you are storing and restoring workspaces, and have been
doing so for a long time. If you type
RNGkind()
what you should see is
[1] "Mersenne-Twister" "Inversion" "Rejection"
but if the .Random.seed is restored from an old session, you might see
[1] "Mersenne-Twister" "Inversion" "Rounding"
The latter uses the buggy version of sample(). Those users should run
RNGkind(sample.kind = "Rejection")
to start using the corrected sampling algorithm. (The default was
changed in R 3.6.0, but if you saved your seed from a previous version,
you'd get the old sampler).
They should also stop reloading old workspaces, but that's another
discussion.
Duncan Murdoch
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