ToLookup Demo

   
 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

public class Employee {
    public string birthYear;
    public string firstName;
    public string lastName;

    public static Employee[] GetActors() {
        Employee[] actors = new Employee[] {
      new Employee { birthYear = "1964", firstName = "K", lastName = "R" },
      new Employee { birthYear = "1968", firstName = "O", lastName = "W" },
      new Employee { birthYear = "1960", firstName = "J", lastName = "S" },
      new Employee { birthYear = "1964", firstName = "S",lastName = "B" },
    };

        return (actors);
    }
}
public class MyStringifiedNumberComparer : IEqualityComparer<string> {
    public bool Equals(string x, string y) {
        return (Int32.Parse(x) == Int32.Parse(y));
    }

    public int GetHashCode(string obj) {
        return Int32.Parse(obj).ToString().GetHashCode();
    }
}
public class MainClass {
    public static void Main() {

        ILookup<string, Employee> lookup = Employee.GetActors()
          .ToLookup(k => k.birthYear, new MyStringifiedNumberComparer());
        IEnumerable<Employee> actors = lookup["1968"];
        foreach (var actor in actors)
            Console.WriteLine("{0} {1}", actor.firstName, actor.lastName);
    }
}