Regex group capture in R with multiple capture-groups

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

str_match(), from the stringr package, will do this. It returns a character matrix with one column for each group in the match (and one for the whole match):

> s = c("(sometext :: 0.1231313213)", "(moretext :: 0.111222)") > str_match(s, "\\((.*?) :: (0\\.[0-9]+)\\)")      [,1]                         [,2]       [,3]           [1,] "(sometext :: 0.1231313213)" "sometext" "0.1231313213" [2,] "(moretext :: 0.111222)"     "moretext" "0.111222"     

Answer 2

gsub does this, from your example:

gsub("\\((.*?) :: (0\\.[0-9]+)\\)","\\1 \\2", "(sometext :: 0.1231313213)") [1] "sometext 0.1231313213" 

you need to double escape the \s in the quotes then they work for the regex.

Hope this helps.