using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var list = new[] {

            new TestClass

            {

                Name = "Mathias",

                BirthDay = new DateTime(1986,1,17),

                Count = 5

            },

            new TestClass

            {

                Name = "Simon",

                BirthDay = new DateTime(1988,1,17),

                Count = 5

            },

                        new TestClass

            {

                Name = "Robbe",

                BirthDay = new DateTime(1987,1,17),

                Count = 5

            },

                        new TestClass

            {

                Name = "Mathias",

                BirthDay = new DateTime(1986,1,17),

                Count = 5

            },

                        new TestClass

            {

                Name = "Mathias",

                BirthDay = new DateTime(1986,1,17),

                Count = 5

            },

                        new TestClass

            {

                Name = "Simon",

                BirthDay = new DateTime(1988,1,17),

                Count = 5

            },

                        new TestClass

            {

                Name = "Robbe",

                BirthDay = new DateTime(1987,1,17),

                Count = 5

            },

        };

        var orderedList = list.OrderByList(t => t.Name, "Mathias", "Robbe", "Simon");

        foreach(var thingy in orderedList)

            Console.WriteLine(thingy.Name);

    }

}

​

public class TestClass

{

    public string Name{get;set;}

    public DateTime BirthDay{get;set;}

    public int Count{get;set;}

}

​

public static class EnumerableExtensions

{

    public static IEnumerable<TSource> OrderByList<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector, params TKey[] list)

    {

        return source.OrderBy(s => Array.IndexOf(list, selector.Invoke(s)));

    }

}