[R] reg expr that retains only bracketed text from strings

[Eric Berger]

Hi Nevil,
Here's one way to do it. (No doubt some regular-expression-gurus will have
more concise ways to get the job done.)

a1 <- sub(".*\\(","\\(",mystrings)
a2 <- sub("\\).*","\\)",a1)
a2[grep("\\(",a2,invert=TRUE)] <- ""
a2

HTH,
Eric




On Wed, Jun 12, 2019 at 8:46 AM nevil amos <nevil.amos using gmail.com> wrote:

> Hi
>
> I am trying to extract only the text contained in brackets from a vector of
> strings
> not all of the strings contain closed bracketed text, they should return an
> empty string or NA
>
> this is what I have at the moment
>
>
> mystrings<-c("ABC","A(B)C","AB(C)")
>
> substring(mystrings, regexpr("\\(|\\)", mystrings))
>
>
> #this returns the whole string  if there are no brackets.
> [1] "ABC"  "(B)C" "(C)"
>
>
> # my desired desired output:
> #    [1]  ""  "(B)" "(C)"
>
> many thanks for any suggestions
> Nevil Amos
>
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>
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