Implementation of XML Information Retrieval by LINQ

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Text.RegularExpressions;

namespace IRProj
{
    public class Tokenizer
    {

        public List<string> Partition(string input)
        {
            List<string> filter = new List<string>();
            Regex r = new Regex("([ \\t{}():;. \n])");
            input = input.ToLower();

            String[] tokens = r.Split(input);           

            for (int i = 0; i < tokens.Length; i++)
            {
                MatchCollection mc = r.Matches(tokens[i]);
                if (mc.Count <= 0 && tokens[i].Trim().Length > 0
                    && !StopWordsHandler.IsStopword(tokens[i]))
                    filter.Add(tokens[i]);
            }
            return filter;
           
        }



    }
}