# [R] string pattern matching

Ulrik Stervbo ulrik.stervbo at gmail.com
Wed Mar 22 07:22:36 CET 2017

```Hi Joe,

you could also rethink your pattern:

grep("x1 \\+ x2", test, value = TRUE)

grep("x1 \\+ x", test, value = TRUE)

grep("x1 \\+ x[0-9]", test, value = TRUE)

HTH
Ulrik

On Wed, 22 Mar 2017 at 02:10 Jim Lemon <drjimlemon at gmail.com> wrote:

> Hi Joe,
>
> test <- c("x1", "x2", "x3", "x1 + x2 + x3")
> multigrep<-function(x1,x2) {
>  xbits<-unlist(strsplit(x1," "))
>  nbits<-length(xbits)
>  xans<-rep(FALSE,nbits)
>  for(i in 1:nbits) if(length(grep(xbits[i],x2))) xans[i]<-TRUE
>  return(all(xans))
> }
> multigrep("x1 + x3","x1 + x2 + x3")
> [1] TRUE
> multigrep("x1 + x4","x1 + x2 + x3")
> [1] FALSE
>
> Jim
>
> On Wed, Mar 22, 2017 at 10:50 AM, Joe Ceradini <joeceradini at gmail.com>
> wrote:
> > Hi Folks,
> >
> > Is there a way to find "x1 + x2 + x3" given "x1 + x3" as the pattern?
> > Or is that a ridiculous question, since I'm trying to find something
> > based on a pattern that doesn't exist?
> >
> > test <- c("x1", "x2", "x3", "x1 + x2 + x3")
> > test
> > [1] "x1"           "x2"           "x3"           "x1 + x2 + x3"
> >
> > grep("x1 + x2", test, fixed=TRUE, value = TRUE)
> > [1] "x1 + x2 + x3"
> >
> >
> > But what if only have "x1 + x3" as the pattern and still want to
> > return "x1 + x2 + x3"?
> >
> > grep("x1 + x3", test, fixed=TRUE, value = TRUE)
> > character(0)
> >
> > I'm sure this looks like an odd question. I'm trying to build a
> > function and stuck on this. Rather than dropping the whole function on
> > the list, I thought I'd try one piece I needed help with...although I
> > suspect that this question itself probably does bode well for my
> > function :)
> >
> > Thanks!
> > Joe
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>

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