R devel - Aug 2019 - Feature request: non-dropping regmatches/strextract

Thank you, I am aware that there are packages that can accomplish this. I
mentioned stringr::str_extract as a function that does not drop empty matches. I
think that the behavior of regmatches(..., regexpr(...))?in base R should permit
an option to prevent dropping of empty matches both for sake of consistency with
the rest of the language (missing data does not yield a dropped index in other
sorts of R functions, and an empty match conceptually corresponds with missing
data) and facility of use in data.frames. The behavior of regmatches(...,
gregexpr(...)) is not objectionable to me, as lists do not drop indices when
they contain character(0) vectors. Alternatively, perhaps this should be
reflected in the (currently non-exported) strextract.

Best,
CG

I'd be happy to entertain patches or at least more specific
suggestions to improve strextract() and strcapture(). I hadn't
exported strextract(), because I wasn't quite sure how it should
behave. This feedback should be helpful.

Thanks,
Michael

On Thu, Aug 29, 2019 at 2:20 PM Cyclic Group Z_1 via R-devel
<r-devel at r-project.org> wrote:
>
> Thank you, I am aware that there are packages that can accomplish this. I
mentioned stringr::str_extract as a function that does not drop empty matches. I
think that the behavior of regmatches(..., regexpr(...)) in base R should permit
an option to prevent dropping of empty matches both for sake of consistency with
the rest of the language (missing data does not yield a dropped index in other
sorts of R functions, and an empty match conceptually corresponds with missing
data) and facility of use in data.frames. The behavior of regmatches(...,
gregexpr(...)) is not objectionable to me, as lists do not drop indices when
they contain character(0) vectors. Alternatively, perhaps this should be
reflected in the (currently non-exported) strextract.
>
> Best,
> CG
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel


-- 
Michael Lawrence
Scientist, Bioinformatics and Computational Biology
Genentech, A Member of the Roche Group
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Thank you! I greatly appreciate your consideration, though of course it is up to
you. I think many people switch to stringr/stringi simply because functions in
those packages have some consistent design choices, for example, they do not
drop empty/missing matches, which facilitates array-based programming. For
example, in the cases where one needs to make a new column in a data.frame
(data.table, tibble, etc.) of regex extractions. Or in any other case where
there needs to be an element-wise correspondence between input and output. I
think insertion of NA_character_ to prevent dropping indices seems like the
natural choice for an array language (which, I think, motivated the creation of
stringr/stringi). While those are great packages and this behavior can be easily
replicated with simple wrappers, string operations are normally easy to
accomplish in base languages, so this seems like something that would be
appropriate to have in base. For example, MATLAB and Pandas regex both allow
non-dropping empty matches (though of course I acknowledge Pandas is not a base
language).

Best,
CG