I am trying to use non-capturing groups with the str_extract function from the stringr package. Here is an example:
library(stringr)
txt <- "foo"
str_extract(txt,"(?:f)(o+)")
This returns
"foo"
while i expect it to return only
"oo"
like in this post: https://stackoverflow.com/a/14244553/3750030
How do i use non-capturing groups in R to remove the content of the groups from the returned value while using it for matching?
When you are using regex (?:f)(o+) this won't Capture but it will match it for sure.
What capturing means is storing in memory for back-referencing, so that it can be used for repeated match in same string or replacing captured string.
like in this post: https://stackoverflow.com/a/14244553/3750030
You misunderstood that answer. Non-Capturing groups doesn't means Non-Matching. It's captured in $1 ( group 1 ) because there is no group prior to it.
If you wish to Only match suppose B followed by A then you should use positive lookbehind like this.
Regex: (?<=f)(o+)
Explanation:
(?<=f) This will look for f to be present behind the following token but won't match.
(o+) This will match and capture as group (here in $1)if previous condition is true.