Regular expression to select repeating groups

Question

I have a series of grouped values that follow a specific format and would like to use a single expression to capture them into groups. For example, I have -group1 -gro

Answer 1

Try this:

(-.+?)(\s|$)

Your first capture group will have what you want (-group1, -group2, etc).

If you want more control over what to allow after the -, change .+? to, for example, [a-zA-Z0-9]+? to only match alphanumeric characters.

Answer 2

You are in luck because C# is one of the few languages (if not the only one) that supports subexpression captures

https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.capture(v=vs.110)

The .NET API can be looked at as follows

 Matches
     Groups (most regex engines stop here)
         Captures (unique for .NET)

It's not clear from your question what you want to match exactly but this should get you started. Ask again if you are stuck.

  string input = "-group1 -group2 ";
  string pattern = @"(-\S*\W){2}";
  foreach (Match match in Regex.Matches(input, pattern))
  {
     Console.WriteLine("Match: {0}", match.Value);
     for (int groupCtr = 0; groupCtr < match.Groups.Count; groupCtr++)
     {
        Group group = match.Groups[groupCtr];
        Console.WriteLine("   Group {0}: {1}", groupCtr, group.Value);
        for (int captureCtr = 0; captureCtr < group.Captures.Count; captureCtr++)
           Console.WriteLine("      Capture {0}: {1}", captureCtr, 
                             group.Captures[captureCtr].Value);
     }                      
  } 

This ouputs

Match: -group1 -group2 
   Group 0: -group1 -group2 
      Capture 0: -group1 -group2 
   Group 1: -group2 
      Capture 0: -group1 
      Capture 1: -group2 

As you can see (Group 1, Capture 0) and (Group 1, Capture 1) offer the individual captures of a group (and not the last as in most languages)

This address I think of what you describe as "to be able to backreference each of the values separately"

(You use the term backreference but I don't think you are aiming for a replacement pattern right?)

Answer 3

With .NET regex (and almost only .NET) you can use:

(?:(-\S+)\s*)+

Group 1 will contain a list of all matched substrings.

Or maybe just using Matches is sufficient in your case:

var re = new Regex(@"-\S+");
var matches = re.Matches(str);