Regular Expressions in C#: An Advanced Lesson

Intro:

Did you Like regular expressions enough from the last post to want to keep reading about some advanced techniques?  Do you like the dwarves from the works of J.R.R Tolkien enough to want to use them in a coding blog?  If you answered yes to both questions then this is your lucky day!

Some advanced techniques:

Lets try to match some arbitrary value, say the dwarf name Gloin and have it followed by any number of digits.  But lets add some trickery to our debacle: not allow the phrase existing in quotes and not allowed within curly brackets like {Gimli Gloin123}.

I'll go ahead and create a regular expression like:  "{[^}]+}|""Gloin\d+""|(Gloin\d+)

The first section within the first set of quotes, {[^}]+}, will match any content between the curly brackets.
The second section, "Gloin\d+", will match any content that exists within those double quotes.
The third seciton, (Gloin\d+) will match Gloin and any digits that succeed it and capture the match into group 1.

Onto some code!

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Collections.Specialized;
using System.Threading.Tasks;

namespace CSharpConsoleAppRegularExpression
{
    class AdvancedTutorial
    {
        static string ConvertToYesNo(bool value)
        {
          if (value)
            return "Yes";
          return "No";
        }

        static void Main()
        {
            string dwarves = @"Gimli"" ""Gloin12"" Gloin11@Gloin22 {4 Gloin42}";
            //string s1 = @"Jane"" ""Tarzan12"" Tarzan11@Tarzan22 {4 Tarzan34}";
            //var myRegex = new Regex(@"{[^}]+}|""Tarzan\d+""|(Tarzan\d+)");
            var myRegex = new Regex(@"{[^}]+}|""Gloin\d+""|(Gloin\d+)");
            var group1Caps = new StringCollection();

            //Match matchResult = myRegex.Match(s1);
            Match matchResult = myRegex.Match(dwarves);
            // put Group 1 captures in a list
            while (matchResult.Success)
            {
              if (matchResult.Groups[1].Value != "")
                group1Caps.Add(matchResult.Groups[1].Value);
              matchResult = matchResult.NextMatch();
            }

            // Task 1: Is there a match?
            Console.WriteLine("*** Is there a Match? ***");
            Console.WriteLine(ConvertToYesNo(group1Caps.Count > 0));

            // Task 2: How many matches are there?
            Console.WriteLine("\n" + "*** Number of Matches ***");
            Console.WriteLine(group1Caps.Count);

            // Task 3: What is the first match?
            Console.WriteLine("\n" + "*** First Match ***");
            if (group1Caps.Count > 0) 
              Console.WriteLine(group1Caps[0]);

            // Task 4: What are all the matches?
            Console.WriteLine("\n" + "*** Matches ***");
            if (group1Caps.Count > 0)
              foreach (string match in group1Caps) 
                 Console.WriteLine(match);

            // Task 5: Replace the matches
            //string replaced = myRegex.Replace(s1, delegate(Match m)
            string replaced = myRegex.Replace(dwarves, delegate(Match m)
            {
              // m.Value is the same as m.Groups[0].Value
              if (m.Groups[1].Value == "") 
                return m.Value;
              return "Thorin";
            });
            Console.WriteLine("\n" + "*** Replacements ***");
            Console.WriteLine(replaced);

            // Task 6: Split
            // Start by replacing by something distinctive,
            // as in Step 5. Then split.
            string[] splits = Regex.Split(replaced, "Thorin");
            Console.WriteLine("\n" + "*** Splits ***");
            foreach (string split in splits) 
              Console.WriteLine(split);

            Console.WriteLine("\nPress Any Key to Exit.");
            Console.ReadKey();
        }
    }
}

Code output:

Final Conclusion

Regular expressions seem to be another slick way of data validation available to developers.  I hope you enjoyed reading this as much as I enjoyed writing this.  Cheers.

Resources:

http://www.rexegg.com/regex-best-trick.html

http://en.wikipedia.org/wiki/List_of_Middle-earth_Dwarves