# [R] string pattern matching

David Winsemius dwinsemius at comcast.net
Wed Mar 22 04:29:01 CET 2017

```> On Mar 21, 2017, at 6:31 PM, Bert Gunter <bgunter.4567 at gmail.com> wrote:
>
> It is not clear to me what you mean, but:
>
>> grep ("x1 \\+.* \\+ x3",test, value = TRUE)
> [1] "x1 + x2 + x3"
>
> ## This will miss "x1 + x3" though.

So then this might be acceptable:

grep ("x1\\ \\+.* x3", test, value = TRUE)

>
> seems to do what you want, maybe. Perhaps you need to read up about
> regular expressions and/or clarify what you want to do.
>
>
> Cheers,
> Bert
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>
>
> On Tue, Mar 21, 2017 at 4:50 PM, 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
>> 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