[R] string pattern matching

[David Winsemius]

> 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
>> 
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> 
> ______________________________________________
> 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.

David Winsemius
Alameda, CA, USA