ValueComparer

ValueComparer.cs

public class ValueComparer<T> : IEqualityComparer<T>
    {
        private readonly Func<T, object>[] _valueSelectors;
        private readonly Func<T, int> _hashCodeFunction;

        public ValueComparer(params Func<T, object>[] valueSelectors)
            : this(t => t.GetHashCode(), valueSelectors)
        {
            _valueSelectors = valueSelectors;
        }

        public ValueComparer(Func<T, int> hashCodeFunction, params Func<T, object>[] valueSelectors)
        {
            _hashCodeFunction = hashCodeFunction;
            _valueSelectors = valueSelectors;
        }

        public bool Equals(T x, T y)
        {
            return _valueSelectors.All(valueSelector => valueSelector(x) == valueSelector(y));
        }

        public int GetHashCode(T obj)
        {
            return _hashCodeFunction(obj);
        }
    }

ValueComparerUsage.cs

            IEnumerable<Contact> contacts = new List<Contact> { 
                new Contact("Tim", "Van Wassenhove"),
                new Contact("Evy", "Penninckx"),
                new Contact("Tiebe", "Van Wassenhove"),
            };

            var distinctLastNames = contacts
                .Distinct(new ValueComparer<Contact>(contact => contact.LastName))
                .Select(contact => contact.LastName);