Removing everything between nested parentheses-CodePudding

For removing everything between parentheses, currently i use:

SELECT 
REGEXP_REPLACE('(aaa) bbb (ccc (ddd) / eee)', "\\([^()]*\\)", "");

Which is incorrect, because it gives bbb (ccc / eee), as that removes inner parentheses only.

How to remove everynting between nested parentheses? so expected result from this example is bbb

CodePudding user response：

In case of Google BigQuery, this is only possible if you know your maximum number of nestings. Because it uses re2 library that doesn't support regex recursions.

let r = /\((?:(?:\((?:[^()])*\))|(?:[^()]))*\)/g
let s = "(aaa) bbb (ccc (ddd) / eee)"
console.log(s.replace(r, ""))

CodePudding user response：

If you can iterate on the regular expression operation until you reach a fixed point you can do it like this:

repeat {
  old_string = string
  string := remove_non_nested_parens_using_regex(string)
} until (string == old_string)

For instance if we have

((a(b)) (c))x)

on the first iteration we remove (b) and (c): sequences which begin with (, end with ) and do not contain parentheses, matched by \([^()]*\). We end up with:

((a) )x)

Then on the next iteration, (a) is gone:

( )x)

and after one more iteration, ( ) is gone:

x)

when we try removing more parentheses, there is no more change, and so the algorithm terminates with x).