Regular Expression pattern to match a math expression

Question

I have the following expression:

"3 + 2 * ((1 + 1 - (2 + 4))) + 112 * 31 - ((1+1) - 14 + 1)"

I want to split the expression with the top level parentesis

For example:

String Expression = "3 + 2 * ((1 + 1 - (2 + 4))) + 112 * 31 - ((1+1) - 14 + 1)";
String[] result = Regex.Split(expression, "??");

Expected output:

//result[0] = 3 + 2 *
//result[1] = (1 + 1 - (2 + 4))
//result[2] = + 112 * 31 -
//result[3] = 3 + 2 *
//result[4] = (1+1) - 14 + 1

Answer 1

This isn't normally a job for regular expressions. However, this msdn blog article suggests that it may be possible in the .net version using an extension called "Balanced Matching".

Not being ac# developer, I don't think I can finish answering, but perhaps this will help.

You might be better off finding or writing an actual parser though.

Answer 2

This regex does what you want since you are using .NET. It uses a feature unique to .NET called balancing groups.

^[^(]*(?=\()|(?<=\()(?>[^()]+|\((?<depth>)|\)(?<-depth>))*(?(depth)(?!))(?=\))|(?(depth)|[^\(\)]+)

The following code:

string expression = "3 + 2 * ((1 + 1 - (2 + 4))) + 112 * 31 - ((1+1) - 14 + 1)";
string pattern = @"^[^(]*(?=\()|(?<=\()(?>[^()]+|\((?<depth>)|\)(?<-depth>))*(?(depth)(?!))(?=\))|(?(depth)|[^\(\)]+)";
MatchCollection results = Regex.Matches(expression,pattern);

Results in the following values populating the results array:

//results[0] = 3 + 2 * 
//results[1] = (1 + 1 - (2 + 4))
//results[2] =  + 112 * 31 - 
//results[3] = (1+1) - 14 + 1

Here is a relevant blog post about balancing groups: http://blog.stevenlevithan.com/archives/balancing-groups

Answer 3

Try with regex:

([^*]+\*)\s*\x28(.+?)\x29\s+([^-]+\-)(.+?)

-

   string a = "3 + 2 * ((1 + 1 - (2 + 4))) + 112 * 31 - ((1+1) - 14 + 1)";
                Match match = Regex.Match(a, @"([^*]+\*)\s*\x28(.+?)\x29\s+([^-]+\-)(.+?)");
                for (int c = 0, len = match.Length; c < len; c++)
                {
                    Console.WriteLine(match.Groups[c].Value);
                }

Well,I have no any better idea of as parsing this.

Answer 4

This one should get what you need:

\(((?>\((?<DEPTH>)|\)(?<-DEPTH>)|.?)*(?(DEPTH)(?!)))\)

Check this article for an overview of "nested constructions": http://www.codeproject.com/KB/recipes/Nested_RegEx_explained.aspx