Distinct list of objects based on an arbitrary key in LINQ

Question

I have some objects:

class Foo {
    public Guid id;
    public string description;
}

var list = new List();
list.Add(new Foo() { id = Guid.Empt         


        

Answer 1

A very elegant and intention revealing option is to define a new extension method on IEnumerable

So you have:

list = list.Distinct(foo => foo.id).ToList();

And ...

    public static IEnumerable Distinct(this IEnumerable list, Func lookup) where TKey : struct {
        return list.Distinct(new StructEqualityComparer(lookup));
    }


    class StructEqualityComparer : IEqualityComparer where TKey : struct {

        Func lookup;

        public StructEqualityComparer(Func lookup) {
            this.lookup = lookup;
        }

        public bool Equals(T x, T y) {
            return lookup(x).Equals(lookup(y));
        }

        public int GetHashCode(T obj) {
            return lookup(obj).GetHashCode();
        }
    }

A similar helper class can be built to compare objects. (It will need to do better null handling)