[R] help with regexp

[Eik Vettorazzi]

Hi Jannis,
just use the backreferences in gsub, see ?gsub, -> replacement

test <- c('filename_1_def.pdf', 'filename_2_abc.pdf')
gsub(".*_([A-z]+)\\.pdf", "\\1", test)

hth.

Am 05.10.2011 13:56, schrieb Jannis:
> Dear list memebers, 
> 
> 
> I am stuck with using regular expressions.
> 
> 
> Imagine I have a vector of character strings like:
> 
> test <- c('filename_1_def.pdf', 'filename_2_abc.pdf')
> 
> How could I use regexpressions to extract only the 'def'/'abc' parts of these strings?
> 
> 
> Some try from my side yielded no results:
> 
> testresults <- grep('(?<=filename_[[:digit:]]_).{1,3}(?=.pdf)', perl = TRUE, value = TRUE)
> 
> Somehow I seem to miss some important concept here. Until now I always used nested sub expressions like:
> 
> testresults <- sub('.pdf$', '', sub('^filename_[[:digit:]]_', '' , test))
> 
> 
> but this tends to become cumbersome and I was wondering whether there is a more elegant way to do this?
> 
> 
> 
> Thanks for any help
> 
> Jannis
> 
> 
> 
> ______________________________________________
> R-help at r-project.org mailing list
> 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.


-- 
Eik Vettorazzi
Institut für Medizinische Biometrie und Epidemiologie
Universitätsklinikum Hamburg-Eppendorf

Martinistr. 52
20246 Hamburg

T ++49/40/7410-58243
F ++49/40/7410-57790

--
Pflichtangaben gemäß Gesetz über elektronische Handelsregister und Genossenschaftsregister sowie das Unternehmensregister (EHUG):

Universitätsklinikum Hamburg-Eppendorf; Körperschaft des öffentlichen Rechts; Gerichtsstand: Hamburg

Vorstandsmitglieder: Prof. Dr. Guido Sauter (Vertreter des Vorsitzenden), Dr. Alexander Kirstein, Joachim Prölß, Prof. Dr. Dr. Uwe Koch-Gromus