R help - May 2006 - Perl-style regexes and capturing results

Just a quick question....

In perl, I can capture parts of a regex like /(\w)\/(\d)/ to get back $1 and
$2 containing the parts of the regex in parentheses.  Is there a parallel in
R?

Thanks,
Sean

gsub and sub support backreferences

sub("(.):(.)", "\\2:\\1", c("1:2",
"5:6")) # c("2:1", "6:5")

# and you can capture them separately using strapply in the gsubfn package
# or perform function-based substitutions using gsubfn.

# Returns: list(c("1", "2"), c("5",
"6"))

library(gsubfn)
strapply(c("1:2", "5:6"), "(.):(.)",
function(z,x,y) c(x,y))

# same
strapply(c("1:2", "5:6"), "(.):(.)", c, backref =
-2)



On 5/4/06, Sean Davis <sdavis2 at mail.nih.gov>
wrote:
> Just a quick question....
>
> In perl, I can capture parts of a regex like /(\w)\/(\d)/ to get back $1
and
> $2 containing the parts of the regex in parentheses.  Is there a parallel
in
> R?
>
> Thanks,
> Sean
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

On Thu, 4 May 2006, Sean Davis wrote:
> Just a quick question....
>
> In perl, I can capture parts of a regex like /(\w)\/(\d)/ to get back $1
and
> $2 containing the parts of the regex in parentheses.  Is there a parallel
in
> R?
Yes.  See ?gsub and especially the examples.  This is not specific to 
Perl, and \1 and \2 are more commonly used, including in R.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595