using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    class Product {

        public string id;

        public string name;

        public string uom;

    }

    public static void Main()

    {

        List<Product> productList = new List<Product>();

        productList.Add(new Product() { id = "one", name = "Some name", uom = "lbs"});

        productList.Add(new Product() { id = "one 1", name = "Some name 1", uom = "mm"});

        productList.Add(new Product() { id = "one 2", name = "Some name 2", uom = "unit"});

        productList.Add(new Product() { id = "one 3", name = "Some name 3", uom = "kg"});

        productList.Add(new Product() { id = "one 4", name = "Some name 4", uom = "lbs"});

        var s = productList.GroupBy(p => p.uom).Select(p => p.Key).ToList();

        s.ForEach( (el) => { Console.WriteLine(el); } );    

        Console.WriteLine("");

    }

}