using System;

using System.Linq;

​

​

class MyObject

{

    public int Id {get; set; }

    public string Name {get; set; }

    public int Age {get; set; }

}

public class Program

{

    public static void Main()

    {

        var data = new [] {

            new MyObject{ Id = 1, Name = "A", Age = 15 },

            new MyObject{ Id = 2, Name = "B", Age = 16 },

            new MyObject{ Id = 1, Name = "C", Age = 17 }

        };

        var result = data.ToDictionary(p => p.Id, p => p.Name);

        foreach(var item in result){

            Console.WriteLine(item.Key);

        }

    }

}