Order object by enum in custom order

Question

I'm trying to rearrange a list of animals in order from medium, large, small. I've been trying to do this with IComparable.CompareTo but I can't figure out how to order it in this specific way. I can only find ways to order by Ascending or Descending values.

My enum:

public enum AnimalSize
    {
        Small = 1, Medium = 3, Large = 5,
    }

My Animal class:

public class Animal : IComparable<Animal>
{
    public bool IsCarnivore;
    public AnimalSize Size;

    public Animal(bool isCarnivore, AnimalSize size)
    {
        this.IsCarnivore = isCarnivore;
        this.Size = size;
    }

    public int CompareTo(Animal other)
    {
        return this.Size.CompareTo(other.Size);
    }

I call the CompareTo from another class where I have a private list of animals.

How can I arrange the animals in order of Medium, Large, Small?

Answer 1

I would not implement IComparable<T> for a non-scalar object such as an animal. What if you want to sort by height instead of size? Or by name? IComparable implies that the object can be converted to a one-dimensional quantity.

Instead, define the sort order you need in an array, and use a simple LINQ query to sort.

public static void Main()
{
    var sampleData = new List<Animal>
    {
        new Animal(false, AnimalSize.Small),
        new Animal(false, AnimalSize.Large),
        new Animal(false, AnimalSize.Medium)
    };

    AnimalSize[] customSortOrder = new[]
    {
        AnimalSize.Small,
        AnimalSize.Medium,
        AnimalSize.Large
    };

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

    foreach (var a in results)
    {
        Console.WriteLine(a.Size);
    }

Output:

Small
Medium
Large

Code on DotNetFiddle