# [R] string pattern matching

Wed Mar 22 14:39:51 CET 2017

```Wow. Thanks to everyone (Jim, Ng Bo Lin, Bert, David, and Ulrik) for
all the quick and helpful responses. They have given me a better
understanding of regular expressions, and certainly answered my
question.

Joe

On Wed, Mar 22, 2017 at 12:22 AM, Ulrik Stervbo <ulrik.stervbo at gmail.com> wrote:
> 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
>> > 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
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>> and provide commented, minimal, self-contained, reproducible code.

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