On Sun, Nov 7, 2010 at 10:15 AM, Dimitris Rizopoulos <d.rizopou...@erasmusmc.nl> wrote: > Dear All, > > I would appreciate any help with the following: given the vector 'x' > > x <- c("Ass1", "Ass.s1", "Ass2", "Ass.s2") > > I would like to pick up the positions where the character string contains > "Ass" but does not contain "Ass.s", so for 'x' that would be positions 1 and > 3. > > I guess this could be programmed around grep() using a suitable regular > expression, but I haven't managed to succeed. >
Assuming that "Ass" appears at most once in each string, as in the example: > x <- c("Ass1", "Ass.s1", "Ass2", "Ass.s2", "Ass.") > grep("Ass(?![.]s)", x, perl = TRUE) [1] 1 3 5 See ?regex for more info. There is also regular expression links in the Links box at http://gsubfn.googlecode.com . -- 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.