On Tue, Sep 28, 2010 at 9:46 AM, Michael Bedward <michael.bedw...@gmail.com> wrote: > What Titus wants to do is akin to retrieving capturing groups from a > Matcher object in Java.
Precisely. Here's the description: http://download.oracle.com/javase/1.4.2/docs/api/java/util/regex/Matcher.html#start(int) Gabor's lookbehind trick solves some special cases but it's not the kind of general solution I'm looking for. Let me explain what I'm trying to achieve here. I'm working on a package that provides tools for processing and analyzing eye movements (we're doing reading research). In most situations, eye movements consist of fixations where the eyes are relatively stationary and saccades, quick movements between fixations. A common way to represent eye movements is as strings of symbols, where each symbol corresponds to a fixation on a particular region. AABC means two fixations followed by a fixation on B and then C. When people analyze eye movements it's often necessary to find specific events in the eye movement record like: fixations on the word C preceded by fixations on words D-F and followed by fixations on words A-C. This event can be specified using this regexpr: "[D-F]+(C)[A-C]+" The group (in parenthesis) indicates the substring for which I'd like to know the position in the overall string. Another application is the extraction of subsequences from a sequence of fixations. Note that in some situations people might have to use more groups in their regexprs and that groups can be nested. In this case the user would have to indicate for which group he/she wants to know the offset. I'm not an expert for regexpr engines but I'm pretty sure the necessary information is available in the engine. Gabor, I see you're the author of gsubfn (fantastic package!). Do you see a relatively simple way to expose information about group offsets and their corresponding match lengths? I think this could be useful for other applications as well. At least it seems Michael could use it, too. We can cook up something for ourselves but a general solution would benefit the larger community. Titus ______________________________________________ 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.