[Rd] Inconsistent results from .C()

[R. Michael Weylandt]

 It might also help if you can point us to the C code to help debug.

MW

On Tue, May 21, 2013 at 10:53 AM, Robin Evans <rje42 at cam.ac.uk> wrote:
> I should add to this that I'm running on Scientific Linux 6.  I later
> noticed that the bug only seems to occur when I run the code from Rstudio,
> and not if I use the terminal directly, so this may be the key to the
> problem.
>
> Robin
>
> On 20 May 2013 16:12, Robin Evans <rje42 at cam.ac.uk> wrote:
>
>> Hello,
>>
>> I've run into a problem which is both maddening and rather hard to
>> replicate, therefore I wondered if someone might know of a plausible
>> explanation for it.  I couldn't find anything in the archives, though
>> maybe I'm searching for the wrong thing.
>>
>> I'm calling some C code using .C, and get the vector I'm interested in
>> back as the 7th location in the returned list.  However I find that if
>> I try to inspect the contents of this entry in the list in some ways,
>> I get one answer, and if I look at it in others I get a different
>> answer.  It's quite possible that there's something wrong with the C
>> code, but this doesn't seem to explain why this phenomenon would occur
>> in R.
>>
>> The problem does not always occur - I have to run the code a few times
>> and then call the console when it does, but the commands below show
>> what can happen when it does.  I apologise for not being able to get a
>> cleaner example.  Full code and output is below, but here is a
>> stylised version:
>>
>> The following all give one answer (which is the wrong answer as far as
>> I'm concerned) :
>>  * printing the whole list :
>>           .C(...)     # and looking at the 7th entry
>>  * applying c() to the 7th element of the list
>>           c(.C(...)[[7]])
>>  * assigning the 7th element to a vector:
>>           x = .C(...)[[7]];
>>           x
>>
>> these give a different answer (which is the answer I would hope the C
>> code returns):
>>  * using dput on the 7th entry:
>>           dput(.C(...)[[7]])
>>  * applying c() and then dput()
>>           dput(c(.C(...)[[7]]))
>>  * just printing the 7th entry of the list
>>           .C(...)[[7]]
>>
>> The answers are consistent in the sense that I always get the same
>> answers from running the same command in the console.  I have tried
>> inspecting the returned objects to see if the objects are somehow of a
>> different class than I expect, or are just being printed oddly, but
>> have not found anything untoward.
>>
>> Any suggestions would be much appreciated!
>>
>> Regards,
>>
>> Robin
>>
>>
>> # THESE COMMANDS GIVE ONE ANSWER
>> # [the correct answer always begins with 1, the incorrect with -1]
>>
>> > .C("oneMargin", c(1L,1L,1L,1L,1L), c(1L,1L,1L,1L,1L), 1L,
>> c(2L,2L,2L,2L,2L), 5L, ptr1, ptr2)[[7]]
>> [1]  1 -1 -1  1 -1  1  1 -1 -1  1  1 -1  1 -1 -1  1 -1  1  1 -1  1 -1
>> -1  1  1 -1 -1  1 -1  1  1 -1
>>
>> > dput(.C("oneMargin", c(1L,1L,1L,1L,1L), c(1L,1L,1L,1L,1L), 1L,
>> c(2L,2L,2L,2L,2L), 5L, ptr1, ptr2)[[7]])
>> c(1L, -1L, -1L, 1L, -1L, 1L, 1L, -1L, -1L, 1L, 1L, -1L, 1L, -1L,
>> -1L, 1L, -1L, 1L, 1L, -1L, 1L, -1L, -1L, 1L, 1L, -1L, -1L, 1L,
>> -1L, 1L, 1L, -1L)
>>
>> > x=dput(c(.C("oneMargin", c(1L,1L,1L,1L,1L), c(1L,1L,1L,1L,1L), 1L,
>> c(2L,2L,2L,2L,2L), 5L, ptr1, ptr2)[[7]]))
>> c(1L, -1L, -1L, 1L, -1L, 1L, 1L, -1L, -1L, 1L, 1L, -1L, 1L, -1L,
>>   -1L, 1L, -1L, 1L, 1L, -1L, 1L, -1L, -1L, 1L, 1L, -1L, -1L, 1L,
>>   -1L, 1L, 1L, -1L)
>> > x
>> [1]  1 -1 -1  1 -1  1  1 -1 -1  1  1 -1  1 -1 -1  1 -1  1  1 -1  1 -1
>> -1  1  1 -1 -1  1 -1  1  1 -1
>>
>> # THESE ALL GIVE A DIFFERENT ONE!
>>
>> > .C("oneMargin", c(1L,1L,1L,1L,1L), c(1L,1L,1L,1L,1L), 1L,
>> c(2L,2L,2L,2L,2L), 5L, ptr1, ptr2)
>>
>> # (OTHER ELEMENTS OF LIST REMOVED)
>> [[7]]
>> [1] -1 -1  1  1  1  1 -1 -1  1  1 -1 -1 -1 -1  1  1  1  1 -1 -1 -1 -1
>> 1  1 -1 -1  1  1  1  1 -1 -1
>>
>> > c(.C("oneMargin", c(1L,1L,1L,1L,1L), c(1L,1L,1L,1L,1L), 1L,
>> c(2L,2L,2L,2L,2L), 5L, ptr1, ptr2)[[7]])
>> [1] -1 -1  1  1  1  1 -1 -1  1  1 -1 -1 -1 -1  1  1  1  1 -1 -1 -1 -1
>> 1  1 -1 -1  1  1  1  1 -1 -1
>> > x = .C("oneMargin", c(1L,1L,1L,1L,1L), c(1L,1L,1L,1L,1L), 1L,
>> c(2L,2L,2L,2L,2L), 5L, ptr1, ptr2)[[7]]
>> > x
>> [1] -1 -1  1  1  1  1 -1 -1  1  1 -1 -1 -1 -1  1  1  1  1 -1 -1 -1 -1
>> 1  1 -1 -1  1  1  1  1 -1 -1
>>
>>
>> --
>> Robin Evans
>> Statistical Laboratory
>> University of Cambridge
>> blog: itsastatlife.blogspot.com
>> web: www.statslab.cam.ac.uk/~rje42
>>
>> Causal Inference Workshop July 15th:
>> http://www.statslab.cam.ac.uk/~rje42/uai13/main.htm
>>
>
>
>
> --
> Robin Evans
> Statistical Laboratory
> University of Cambridge
> blog: itsastatlife.blogspot.com
> web: www.statslab.cam.ac.uk/~rje42 <http://www.stat.washington.edu/~rje42>
>
> Causal Inference Workshop July 15th:
> http://www.statslab.cam.ac.uk/~rje42/uai13/main.htm
>
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>
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