C# Regex - How to remove multiple paired parentheses from string

Question

I am trying to figure out how to use C# regular expressions to remove all instances paired parentheses from a string. The parentheses and all text between them should be removed. The parentheses aren't always on the same line. Also, their might be nested parentheses. An example of the string would be

This is a (string). I would like all of the (parentheses
to be removed). This (is) a string. Nested ((parentheses) should) also
be removed. (Thanks) for your help.

The desired output should be as follows:

This is a . I would like all of the . This  a string. Nested  also
be removed.  for your help.

... or here: http://stackoverflow.com/questions/133601/can-regular-expressions-be-used-to-match-nested-patterns — James Boutcher, Jan 18 '13 at 21:23
I don't think it is a duplicate, as I am also asking about normal non-nested parentheses and parenthesis that span more than one line in addition to the nested portion. If the nested portion can't be done, I'd still be interested in the other two. — Matt Brandon, Jan 18 '13 at 21:24
The "duplicate question" does not have an answer - and there **IS** an answer. — JDB, Jan 19 '13 at 02:41

Tim Pietzcker · Accepted Answer · 2013-01-19T14:53:43.093

22

Fortunately, .NET allows recursion in regexes (see Balancing Group Definitions):

Regex regexObj = new Regex(
    @"\(              # Match an opening parenthesis.
      (?>             # Then either match (possessively):
       [^()]+         #  any characters except parentheses
      |               # or
       \( (?<Depth>)  #  an opening paren (and increase the parens counter)
      |               # or
       \) (?<-Depth>) #  a closing paren (and decrease the parens counter).
      )*              # Repeat as needed.
     (?(Depth)(?!))   # Assert that the parens counter is at zero.
     \)               # Then match a closing parenthesis.",
    RegexOptions.IgnorePatternWhitespace);

In case anyone is wondering: The "parens counter" may never go below zero (<?-Depth> will fail otherwise), so even if the parentheses are "balanced" but aren't correctly matched (like ()))((()), this regex will not be fooled.

For more information, read Jeffrey Friedl's excellent book "Mastering Regular Expressions" (p. 436)

edited Jan 19 '13 at 14:53

answered Jan 18 '13 at 21:26

Tim Pietzcker

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@MattBrandon - There is an even easier way to do this in .NET: [Balancing Group Definitions](http://msdn.microsoft.com/en-us/library/bs2twtah.aspx#balancing_group_definition). – JDB Jan 19 '13 at 02:39
@Cyborgx37: What do you mean by "an even easier way"? I *am* using exactly the technique you linked to (thanks for the link - I've included it in my answer). I just use a different name for the counter (`Depth` instead of `Open`) which is of course irrelevant. – Tim Pietzcker Jan 19 '13 at 07:52
Also, I usually don't worry about downvotes, but in this case I would be very interested in learning why this answer has been deemed "not helpful" by someone. – Tim Pietzcker Jan 19 '13 at 07:53

score 2 · Answer 2 · answered Jan 18 '13 at 21:26

2

You can repetitively replace /\([^\)\(]*\)/g with the empty string till no more matches are found, though.

answered Jan 18 '13 at 21:26

flup

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score 1 · Answer 3 · answered Jan 18 '13 at 21:28

1

How about this: Regex Replace seems to do the trick.

string Remove(string s, char begin, char end)
{
    Regex regex = new Regex(string.Format("\\{0}.*?\\{1}", begin, end));
    return regex.Replace(s, string.Empty);
}


string s = "Hello (my name) is (brian)"
s = Remove(s, '(', ')');

Output would be:

"Hello is"

answered Jan 18 '13 at 21:28

Botonomous

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I think you'd be better off using `Regex.Escape()` over `"\\{0}"` – JDB Jan 19 '13 at 02:47

score 1 · Answer 4 · answered Jan 18 '13 at 21:30

1

Normally, it is not an option. However, Microsoft does have some extensions to standard regular expressions. You may be able to achieve this with Grouping Constructs even if it is faster to code as an algorithm than to read and understand Microsoft's explanation of their extension.

answered Jan 18 '13 at 21:30

Alexandre Rafalovitch

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I actually ended up solving this problem earlier today by just coding an algorithm to do the work. However, it left me very curious as to whether or not it could be done with Regex – Matt Brandon Jan 18 '13 at 21:37

C# Regex - How to remove multiple paired parentheses from string

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