using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Customer c1 = new Customer() { ID = 1, Name = "Mike", Salary = 5000 };

            Customer c2 = new Customer() { ID = 2, Name = "John", Salary = 6500 };

            Customer c3 = new Customer() { ID = 3, Name = "Steve", Salary = 3500 };

​

            List<Customer> listOfCustomers = new List<Customer>();

            listOfCustomers.Add(c1);

            listOfCustomers.Add(c2);

            listOfCustomers.Add(c3);

​

            var dictionary = Customer.ToDictionary(x=>x.ID, listOfCustomers);

        foreach(KeyValuePair<int,Customer> pair in dictionary)

        {

            Console.WriteLine($"Key: {pair.Key}, Value={pair.Value}");

        }

    }

}

​

public class Customer

    {

        public int ID { get; set; }

        public string Name { get; set; }

        public int Salary { get; set; }

​

        public static Dictionary<TKey, Customer> ToDictionary<TKey>(Func<Customer,TKey> filter,List<Customer> customers)

        {

​

            var dictionary = new Dictionary<TKey, Customer>();

​

            foreach(var item in customers)

            {

                dictionary.Add(filter.Invoke(item),item);

            }

​

            return dictionary;

        }

    }