[R] Regular expressions

Peter Dalgaard p.dalgaard at biostat.ku.dk
Wed Jan 11 19:23:41 CET 2006

"Ales Ziberna" <aleszib at gmail.com> writes:

> Matching regular expressions
> Dear useRs!
> I have the following problem. I would like to find objects in my environment
> that have two strings in it. For example, I might want to find objects that
> have in their names "MY" and "TARGET". I do not care about the ordering of
> these two substrings in the name, neither what is in front, behind or
> between them, the only thing important is that both words are present. I
> apologize if this is covered in help pages (then I did not understand it by
> reading them several times) or it was answered previously (then I did not
> find it).
> Since "ls" with argument pattern essentially uses "grep" (if I am not
> mistaken), I have an example for "grep"
> text<-c("somethigMYsomthing elseTARGET another thing","MY somthing TARGET
> another thing","somethig somthing elseTARGETMY another
> thing","somethigMTARGETY another thing")
> grep(pattern="MY&TARGET", x=text)
> #I would like to get 1 2 3  and not 4 or actually their names using
> text[grep(pattern="MY&TARGET", x=text)]
> #of course, the "pattern" in this case is wrong
> I know I can do
> text[grep(pattern="MY", x=text)][grep(pattern="TARGET",
> x=text[grep(pattern="MY",x=text)])] 
> However I hope there exists a more elegant way.

Perhaps this?

text[intersect(grep("MY",text), grep("TARGET",text))]

   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

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