Whats the Difference Between MatchCollection and..

chobo2 · May 19th, 2008, 03:58 PM

Hi

I am doing Regular expressions right now in C# and I don't understand which Collection should I be using?

Like I seen a couple different tutorials some Using MatchCollection and some using GroupCollection. I don't know when I should be using what.

Like Here are some ways I seen to do it.

// This is my own try at it.

Code:

  string asinPattern = "reg Expression Here;
        Regex MyRegex = new Regex(asinPattern,
      RegexOptions.IgnoreCase
      | RegexOptions.Multiline
      | RegexOptions.CultureInvariant
      | RegexOptions.IgnorePatternWhitespace
      | RegexOptions.Compiled
      );

        MatchCollection matchAsin = MyRegex.Matches(result);

        for (int i = 0; i < matchAsin.Count; i++)
            {
                // Group g = matchAsin[i];
                Match g = matchAsin[i];
                Test.Add(g.Value);
            }

So first what Is the difference between using Group or Match. They both seem to get the same result.

The second way I see it is with a for each loop.

Code:

MatchCollection matches = rx.Matches(text);
    foreach (Match match in matches)
        {
            GroupCollection groups = match.Groups;
            Console.WriteLine("'{0}' repeated at positions {1} and {2}",  
                              groups["word"].Value, 
                              groups[0].Index, 
                              groups[1].Index);
        }

So this one I don't understand why they first put in a match collection then a groupCollection. It seems kinda pointless to me. To keep put it in a another collection one at a time. So I got to be missing something.

http://msdn.microsoft.com/en-us/libr...ollection.aspx

Then finally I seen

Code:

using System.Text.RegularExpressions;

class Reg{
    public static void Main(){
        // Should match everything except the last two.
        string str = "$1.57 $316.15 $19.30 $0.30 $0.00 $41.10 $5.1 $.5";
        string strMatch = @"\$(\d+)\.(\d\d)";

        for ( Match m = Regex.Match( str, strMatch ); m.Success; m = m.NextMatch() ){
            GroupCollection gc = m.Groups;

            System.Console.WriteLine( "The number of captures: " + gc.Count );
            // Group 0 is the entire matched string itself
            // while Group 1 is the first group to be captured.
            for ( int i = 0; i < gc.Count; i++ ){
                Group g = gc[i];
                System.Console.WriteLine( g.Value );
            }
        }
    }
}

Where they use Group and GroupCollection. 

So when should I use each scenario? 

Thanks

samjudson · May 19th, 2008, 04:24 PM

Generally I would say that you use a MatchCollection if you want to find any number of strings that match a particular regular expression. Each Match will be a match against the whole regular expression.

Groups can be a sub-part of a regular expression, captured inbetween parenthasis '()'.

So in the example above they want to match a dollar, followed by a number, then a period, then another number. Each instance of this sequence is a match. Within each match the first number and the second number are wrapped in parenthasis so they form two seperate groups.

Just to confuse matters a little the first group (gc[0] in the above example) will be the whole match.

/- Sam Judson : Wrox Technical Editor -/

chobo2 · May 19th, 2008, 05:06 PM

So you might be using both Match Collection and General Collection together? Since you Might first want to get all the Matches and then break each Match down into Groups.

What does Capture Collection do then?

Thanks