# [R] string pattern matching

Jim Lemon drjimlemon at gmail.com
Wed Mar 22 01:43:10 CET 2017

```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")
 TRUE
multigrep("x1 + x4","x1 + x2 + x3")
 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
>  "x1"           "x2"           "x3"           "x1 + x2 + x3"
>
> grep("x1 + x2", test, fixed=TRUE, value = TRUE)
>  "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
>
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