Regex group capture in R with multiple capture-groups

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"    

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.