using System;

using System.Linq;

using System.Collections.Generic;

​

public class Product {

    public string ProductCode {get;set;}

    public string UserImportId {get;set;}

    public string NameCustomer {get;set;}

}

public class Simple {

  public static void Main() {

    string[] names = { "Burke", "Laptop", "Computer", 

                       "Mobile", "Ahemed", "Sania", 

                       "Kungada", "David","United","Sinshia" };

​

    var  query = from s in names 

                               where s.Length == 6

                               orderby s

                               select s.ToUpper();

​

    foreach (string item in query)

      Console.WriteLine(item);

    var products = new List<Product>

    {

        new Product {ProductCode = "FICO", UserImportId = "111", NameCustomer = "NGUYEEN KIEM" },

        new Product {ProductCode = "FICO", UserImportId = "111", NameCustomer = "Bùi Minh Huy" },

​

        new Product {ProductCode = "XXX", UserImportId = "111", NameCustomer = "DINH GIO" },

        new Product {ProductCode = "XXX", UserImportId = "111", NameCustomer = "TRONG HOANG" },

        new Product {ProductCode = "ZZZ", UserImportId = "111", NameCustomer = "TAM MAO" },

    };

    var groupBy = products.GroupBy(g => new {g.ProductCode, g.UserImportId}).First().Select(x => x);

         foreach (var item in groupBy)

      Console.WriteLine(item.NameCustomer);

  }

}