Regex group capture in R with multiple capture-gro

Question

In R, is it possible to extract group capture from a regular expression match? As far as I can tell, none of grep, grepl, regexpr, gregexpr, sub, or gsub return the group captures.

I need to extract key-value pairs from strings that are encoded thus:

\((.*?) :: (0\.[0-9]+)\)

I can always just do multiple full-match greps, or do some outside (non-R) processing, but I was hoping I can do it all within R. Is there's a function or a package that provides such a function to do this?

Answer 1

Try regmatches() and regexec():

regmatches("(sometext :: 0.1231313213)",regexec("\\((.*?) :: (0\\.[0-9]+)\\)","(sometext :: 0.1231313213)"))
[[1]]
[1] "(sometext :: 0.1231313213)" "sometext"                   "0.1231313213"

Answer 2

I like perl compatible regular expressions. Probably someone else does too...

Here is a function that does perl compatible regular expressions and matches the functionality of functions in other languages that I am used to:

regexpr_perl <- function(expr, str) {
  match <- regexpr(expr, str, perl=T)
  matches <- character(0)
  if (attr(match, 'match.length') >= 0) {
    capture_start <- attr(match, 'capture.start')
    capture_length <- attr(match, 'capture.length')
    total_matches <- 1 + length(capture_start)
    matches <- character(total_matches)
    matches[1] <- substr(str, match, match + attr(match, 'match.length') - 1)
    if (length(capture_start) > 1) {
      for (i in 1:length(capture_start)) {
        matches[i + 1] <- substr(str, capture_start[[i]], capture_start[[i]] + capture_length[[i]] - 1)
      }
    }
  }
  matches
}