LINQ - Group by in C#

using System;
using System.Linq;
using System.Xml.Linq;

namespace ForgetCode
{   
    public class MainClass
    {
        public static void Main()
        {
            dat customers = new dat(@"c:\data.mdf");

            // queryCustomersByCity is an IEnumerable<IGrouping<string, Customer>> 
            var queryCustomersByCity =
                from cust in customers
                group cust by cust.City;

            // customerGroup is an IGrouping<string, Customer> 
            foreach (var customerGroup in queryCustomersByCity)
            {
                Console.WriteLine(customerGroup.Key);
                foreach (Customer customer in customerGroup)
                {
                    Console.WriteLine("    {0}", customer.Name);
                }
            }
            
        }
    }
}