Some Random LINQ Snippet I needed

LinqSnippet.cs

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

namespace LinqSnippet
{
    public class LinqSnippet
    {
        public void Test()
        {
            var oldlines = new[] {"xxx", "a b 1", "a c 2", "b a 3"};
            var newlines = new[] {"a b 2", "a c 2", "b b 1"};

            var results =
                from oldline in oldlines.ToDict()
                join newline in newlines.ToDict()
                    on oldline.Key equals newline.Key
                where oldline.Value != newline.Value
                select oldline.Key;

            var x = results.ToArray();
        }
    }

    public static class EnumerableEx
    {
        public static Dictionary<string, string> ToDict(this IEnumerable<string> oldlines)
        {
            var regex = new Regex(@"^(\w+\s+\w+)\s+(\w+)$");
            var oldMatches = oldlines
                .Select(line => regex.Match(line))
                .Where(match => match.Success)
                .Select(match => match.Groups
                                     .Cast<Group>()
                                     .Select(group => group.Value)
                                     .ToArray())
                .ToDictionary(groups => groups[1], groups => groups[2]);
            return oldMatches;
        }
    }
}