public class Car
    {
        public long ID { get; set; }
        public string Name { get; set; }
        public string OtherName { get; set; }
    }

static void Main(string[] args)
        {
            List<Car> cars = new List<Car>();
            cars.Add(new
 
 Car() { ID = 1, Name = "紅旗", OtherName = "hq1" });
            cars.Add(new Car() { ID = 2, Name = "賓士", OtherName = "bc1" });
            cars.Add(new Car() { ID = 3, Name = "寶馬", OtherName = "bm1" });
            cars.Add(new Car() { ID = 4, Name = "賓士", OtherName = "bc2" });
            cars.Add(
 
new Car() { ID = 5, Name = "寶馬", OtherName = "bm2" });


            //同名
            var carSame = cars.GroupBy(x => x.Name).Where(x => x.Count() > 1).ToList();
            foreach (var item in carSame)
            {
                Console.WriteLine(item.Key);
            }


            Console.WriteLine(
 
"---*---");
            var carSameArr = cars.GroupBy(x => x.Name).Where(x => x.Count() > 1).Select(i => i.Key).ToArray();
            foreach (string car in carSameArr)
            {
                Console.WriteLine(car);
            }


            Console.WriteLine("---*---");
            var carDict = cars.GroupBy(x => x.Name).ToDictionary(x => x.Key, x => x.ToList());
            //以下是輸出：
            foreach (KeyValuePair<string, List<Car>> pair in carDict)
            {
                Console.WriteLine(pair.Key);
                pair.Value.ForEach(x => Console.WriteLine(@"ID={0}, Name='{1}',OtherName='{2}'", x.ID, x.Name, x.OtherName));
                Console.WriteLine();
            }

            Console.ReadKey();
        }

參考：