On Mon, Sep 27, 2010 at 11:48 AM, Titus von der Malsburg <malsb...@gmail.com> wrote: > Dear list! > >> gregexpr("a+(b+)", "abcdaabbc") > [[1]] > [1] 1 5 > attr(,"match.length") > [1] 2 4 > > What I want is the offsets of the matches for the group (b+), i.e. 2 > and 7, not the offsets of the complete matches. Is there a way in R > to get that? > > I know about gsubgn and strapply, but they only give me the strings > matched by groups not their offsets. > > I could write something myself that first takes the above matches > ("ab" and "aabb") and then searches again using only the group (b+). > For this to work, I'd have to parse the regular expression and search > several times (> 2, for nested groups) instead of just once. But I'm > sure there is a better way to do this. >
Try this zero width negative look behind expression: > gregexpr("(?!a+)(b+)", "abcdaabbc", perl = TRUE) [[1]] [1] 2 7 attr(,"match.length") [1] 1 2 See ?regexp for more info. -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com ______________________________________________ R-help@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.