capture-group

I want to provide alternative replacement patterns to re.sub. Let's say i've got two search patterns as alternatives, like this: re.sub(r"[A-Z]+|[a-z]+", replacementpattern, string) and instead of providing one replacement pattern I would like to somehow catch which search pattern alternative was matched and provide alternative replacement patterns. Is this possible? Thanks. PS. code specifics here are irrelevant, it's a general question. You can pass a function to re.sub() . In the function you can return the value needed based on the captured group. A simple code for illustration: >>> def

Are optional non-capturing groups redundant? Is the following regex: (?:wo)?men semantically equivalent to the following regex? (wo)?men Your (?:wo)?men and (wo)?men are semantically equivalent, but technically are different, namely, the first is using a non-capturing and the other a capturing group. Thus, the question is why use non-capturing groups when we have capturing ones ? Non-caprturing groups are of help sometimes. To avoid excessive number of backreferences (remember that it is sometimes difficult to use backreferences higher than 9) To avoid the problem with 99 numbered

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? str_match() , from the stringr package, will do this. It returns a character matrix with one column for each