using System;

using System.Linq;

using System.Collections.Generic;

​

​

public enum AnimalSize

    {

        Small = 1, Medium = 3, Large = 5,

    }

​

public class Animal

{

    public bool IsCarnivore;

    public AnimalSize Size;

​

    public Animal(bool isCarnivore, AnimalSize size)

    {

        this.IsCarnivore = isCarnivore;

        this.Size = size;

    }

}

​

public class Program

{

    public static void Main()

    {

        AnimalSize[] orderBy = new[]

        {

            AnimalSize.Small,

            AnimalSize.Medium,

            AnimalSize.Large

        };

        var sampleData = new List<Animal>

        {

            new Animal(false, AnimalSize.Small),

            new Animal(false, AnimalSize.Large),

            new Animal(false, AnimalSize.Medium)

        };

        var results = sampleData.OrderBy( a => Array.IndexOf(orderBy, a.Size ) );

        foreach (var a in results)

        {

            Console.WriteLine(a.Size);

        }

    }

}