Extending IEnumerable With Reflection To Create A Custom Distinct Method

Reflection is a great tool when it comes to handling the information at runtime. I found this solution below to be suitable in one of my applications because I wanted something that I could easily adapt.

The implementation of the method below looks for both public and private fields and properties.

 public static partial class Extensions
    {
        public static IEnumerable DistinctBy<T, Tkey>(this IEnumerable @this, Expression<Func<T, object>> expression)
        {
            string binding = ReflectObj.ObjGetPropertyPath(expression);
            return DistinctBy<T, Tkey>(@this, binding);
        }
        public static IEnumerable DistinctBy<T, Tkey>(this IEnumerable @this, string binding)
        {
            string[] _params = binding.Split('.');
            IList list = new List();
            IList ReturnList = new List();
            //
            foreach (var item in @this)
            {
                //get key
                object Key = item;
                foreach (var _param in _params)
                {
                    Type t = Key.GetType();
                    PropertyInfo pi = t.GetProperty(_param, BindingFlags.Public | BindingFlags.Instance);
                    Key = pi.GetValue(Key);
                }
                if (list.Where(x => x.Equals(Key)).Count() == 0)
                {
                    list.Add((Tkey)Key);
                    ReturnList.Add(item);
                }
                list.Add((Tkey)Key);
            }
            return ReturnList;
        }
    }

Let’s create a product class that has a Price. We aim to easily create a list with unique “parameters” that will be defined in a string.

class Price  
    {  
        public double Value { get; set; }  
    }  
    class Product  
    {  
        public string Name { get; set; }  
        public Price Price { get; set; }  
        private int NoPrice;  
    }  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            List Products = new List  
            {  
                new Product{ Name = "Product1", Price = new Price{ Value = 100} },  
                new Product{ Name = "Product2", Price = new Price{ Value = 100} },  
                new Product{ Name = "Product3", Price = new Price{ Value = 200} }  
            };  
            // will result 1 item, NoPrice default for all is 0  
            var DistinctProducts1 = Products.DistinctBy<Product, int>("NoPrice");  
            // will result 3 items, no such key is found  
            var DistinctProducts2 = Products.DistinctBy<Product, int>("NoPrice.Test");  
            // will result 2 items - Value is 100 for 2 of them  
            var DistinctProducts3 = Products.DistinctBy<Product, int>("Price.Value");  
        }  
    }  
}