using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public class Item

    {

        public int Id {get;set;}

    }

    public static void Main()

    {

        var master = (new []{ 1, 2, 3, 4, 5}).Select(x => new Item {Id = x});

        var update  = (new []{ 1, 3, 5}).Select(x => new Item {Id = x});

        master = master.Intersect(update, new KeyEqualityComparer<Item>(s => s.Id));

        foreach (var item in master)

        {

            Console.WriteLine(item.Id);

        }

    }

    public class KeyEqualityComparer<T> : IEqualityComparer<T>

    {

        private readonly Func<T, object> keyExtractor;

​

        public KeyEqualityComparer(Func<T, object> keyExtractor)

        {

            this.keyExtractor = keyExtractor;

        }

​

        public bool Equals(T x, T y)

        {

            return this.keyExtractor(x).Equals(this.keyExtractor(y));

        }

​

        public int GetHashCode(T obj)

        {

            return this.keyExtractor(obj).GetHashCode();

        }

    }

}