R devel - Feb 2023 - An interesting chat with ChatGPT

I was wondering which anchor would match in the regular expression 
"(a)|(b)" if both "a" and "b" matches the target
string.  What appears
to happen is that the first match wins, and that's how it is documented 
in Python, but I was looking for docs on this in R.

As far as I can see, the ?regex help page doesn't resolve this. So just 
for fun, I decided to ask ChatGPT, and got an interesting response.  I 
won't show the whole conversation here, but just some extracts:

---------------------------------------
Me:  In a regular expression in R, if both "a" and "b"
match, which does
"(a)|(b)" match?  Please include authoritative references in your
answer.

ChatGPT: [long answer about grep]

Me:  In grep(), it doesn't matter which of a or b matches.  It's only in
sub() or gsub() that it makes a difference.  Do you know an 
authoritative reference that discusses those functions?

ChatGPT:  [long irrelevant answer about sub and gsub, with a reference 
to "R Cookbook" by P. Teetor.]

Me:  Teetor's book is not authoritative, and the other reference doesn't
discuss ambiguous alternation.

... finally we get to the interesting part ...

ChatGPT: I apologize for the mistake in my previous answer.

A more authoritative reference for the behavior of regular expressions 
in R can be found in the official R documentation.

Regarding the behavior of ambiguous alternation, the regex section of 
the manual "An Introduction to R" explains it as follows:

"When several alternatives are possible, the first alternative is 
chosen, so it is important to specify alternatives in the order in which 
they should be tried."

Here is the reference for the official R documentation:

     "An Introduction to R" manual: 
https://cran.r-project.org/doc/manuals/r-release/R-intro.html#Regular-expression-facilities

I hope this reference provides the information you were looking for.
---------------------------------------


All right, an authoritative answer!  The only problem is that *it 
doesn't exist*.  There's no such anchor in that document.  R-intro
isn't
a very rapidly changing document, so I could look at every change 
recorded in svn, and that section has *never* existed.

I guess ChatGPT is a pattern matching machine, and if such a question 
had an answer, it would probably be in a location like that.  (I would 
have guessed a help page like ?regex instead of R-intro, but I had just 
told it that answer was wrong.)

Duncan Murdoch

Duncan -

Indeed, this has now been well documented; I have called these constructions
"Schr?dinger Facts", since they arise from a superposition of truths
in the training data that collapse into an untruth when observed.

   https://sentientsyllabus.substack.com/p/chatgpts-achilles-heel

Now, the curious question is: why can it program. Why is its production of
R-syntax less vulnerable to this effect than a literature quote, or reference?
Maybe it has to do with the fact that in producing correct syntax there is a
ground truth - errors just will not run. But I'm not sure.

Regardless: it signals that we need a reinvigorated culture of validation.
Actually ChatGPT will happily make test data for you. Whisvh. in a way, it judt
did  ;-)


Boris



> On 2023-02-13, at 08:37, Duncan Murdoch <murdoch.duncan at gmail.com>
wrote:
> 
> I was wondering which anchor would match in the regular expression
"(a)|(b)" if both "a" and "b" matches the target
string.  What appears to happen is that the first match wins, and that's how
it is documented in Python, but I was looking for docs on this in R.
> 
> As far as I can see, the ?regex help page doesn't resolve this. So just
for fun, I decided to ask ChatGPT, and got an interesting response.  I won't
show the whole conversation here, but just some extracts:
> 
> ---------------------------------------
> Me:  In a regular expression in R, if both "a" and "b"
match, which does "(a)|(b)" match?  Please include authoritative
references in your answer.
> 
> ChatGPT: [long answer about grep]
> 
> Me:  In grep(), it doesn't matter which of a or b matches.  It's
only in sub() or gsub() that it makes a difference.  Do you know an
authoritative reference that discusses those functions?
> 
> ChatGPT:  [long irrelevant answer about sub and gsub, with a reference to
"R Cookbook" by P. Teetor.]
> 
> Me:  Teetor's book is not authoritative, and the other reference
doesn't discuss ambiguous alternation.
> 
> ... finally we get to the interesting part ...
> 
> ChatGPT: I apologize for the mistake in my previous answer.
> 
> A more authoritative reference for the behavior of regular expressions in R
can be found in the official R documentation.
> 
> Regarding the behavior of ambiguous alternation, the regex section of the
manual "An Introduction to R" explains it as follows:
> 
> "When several alternatives are possible, the first alternative is
chosen, so it is important to specify alternatives in the order in which they
should be tried."
> 
> Here is the reference for the official R documentation:
> 
>    "An Introduction to R" manual:
https://cran.r-project.org/doc/manuals/r-release/R-intro.html#Regular-expression-facilities
> 
> I hope this reference provides the information you were looking for.
> ---------------------------------------
> 
> 
> All right, an authoritative answer!  The only problem is that *it
doesn't exist*.  There's no such anchor in that document.  R-intro
isn't a very rapidly changing document, so I could look at every change
recorded in svn, and that section has *never* existed.
> 
> I guess ChatGPT is a pattern matching machine, and if such a question had
an answer, it would probably be in a location like that.  (I would have guessed
a help page like ?regex instead of R-intro, but I had just told it that answer
was wrong.)
> 
> Duncan Murdoch
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

--
Boris Steipe MD, PhD

Professor em.
Department of Biochemistry 
Temerty Faculty of Medicine
University of Toronto