Regular expression to select 2 kinds of substrings - r

Question

I have strings like:
\n A vs B \n
\n C vs D (EF) \n
\n GH ( I vs J) \n
in a vector called myData.
The following is myData.
c("\n A vs B \n", "\n C vs D (EF) \n", "\n GH ( I vs J)\n")
I want to select A vs B from 1, C vs D from 2 and I vs J from 3.
I have the following code:
loc = regexpr(".*vs.*|\\(.*vs.*\\)",myData,ignore.case=TRUE,perl=T)
end = loc + attr(loc,"match.length")-1
substr(myData,loc,end)
which gives three output:
[1] " A vs B " " C vs D (EF) " " GH ( I vs J)"
The last match is incorrect. How can I fix this?

Answer 1

We can use str_extract
library(stringr)
str_extract(str1, "[A-Za-z]\\s*vs\\s*[A-Za-z]")
#[1] "A vs B" "C vs D" "I vs J"
Or if there are other lower case characters in place of 'vs'
str_extract(str1, "[A-Z]\\s*[a-z]+\\s*[A-Z]")
#[1] "A vs B" "C vs D" "I vs J"
Or with sub from base R
sub(".*([A-Z]\\s*[a-z]+\\s*[A-Z]).*", "\\1", str1)
#[1] "A vs B" "C vs D" "I vs J"
data
str1 <- c("\n A vs B \n", "\n C vs D (EF) \n", "\n GH ( I vs J)\n")

Answer 2

You may use the base R regmatches / gregexpr solution using a PCRE regex like yours, but using lookarounds, changing . to [^()] (to avoid the overflow across parentheses) and placing the longer alternative before the smaller one:
> myData <- c("\n A vs B \n", "\n C vs D (EF) \n", "\n GH ( I vs J)\n")
> res <- regmatches(myData, gregexpr("(?<=\\()[^()]*vs[^()]*(?=\\))|[^()]*vs[^()]*", myData, perl=TRUE))
> trimws(res)
[1] "A vs B" "C vs D" "I vs J"
See the R online demo
Details:
(?<=\\() - positive lookbehind making sure there is a ( immediately to the left of the current location
[^()]* - 0+ chars other than ( and )
vs - a literal substring
[^()]* - 0+ chars other than ( and )
(?=\\)) - positive lookahead making sure there is a ) immediately to the right of the current location
| - or
[^()]*vs[^()]* - a vs enclosed with 0+ chars other than ( and )
NOTE: If you need to prevent the overflow across lines, you need to add \r\n to the [^()] -> [^()\r\n].
See this regex demo.

Answer 3

Throwing a non-regex approach in the mix. Basically we split at vs and paste tha last character of the first element with the first character of the second element.
sapply(strsplit(x, ' vs '), function(i)
paste0(substr(i[1], nchar(i), nchar(i)), ' Vs ', substr(i[2], 1, 1)))
#[1] "A Vs B" "C Vs D" "I Vs J"