R help - May 2020 - Question about "sample" function and inconsistent results I am getting across machines.

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.

Sincerely,

Tom Fomby

Professor of Economics

SMU

Dallas, TX 75275

tfomby at smu.edu


	[[alternative HTML version deleted]]

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

It is a lot easier from this side of the conversation to view skeptically the
claim that all of these installations of R are using the same version than that
the software seed has started behaving randomly within the same version of R.

On May 2, 2020 10:39:58 PM PDT, "Fomby, Tom" <tfomby at
mail.smu.edu> 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.
>
>Sincerely,
>
>Tom Fomby
>
>Professor of Economics
>
>SMU
>
>Dallas, TX 75275
>
>tfomby at smu.edu
>
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
-- 
Sent from my phone. Please excuse my brevity.

I just tried both versions, and it's the ASUS that's using the buggy old
algorithm.

Duncan Murdoch

On 03/05/2020 3:32 p.m., Duncan Murdoch wrote:
> 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
>

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.

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.

Thank you,

Tom Fomby

Department of Economics

SMU

Dallas, TX 75275


________________________________
From: Duncan Murdoch <murdoch.duncan at gmail.com>
Sent: Sunday, May 3, 2020 2:32 PM
To: Fomby, Tom; r-help at 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

	[[alternative HTML version deleted]]