如何使用 LINQ 查找特定属性的重复项？

Customer customerOne = new Customer("John", "Doe");
Customer customerTwo = new Customer("Super", "Man");
Customer customerThree = new Customer("Crazy", "Guy");
Customer customerFour = new Customer("Jane", "Doe");
Customer customerFive = new Customer("Bat", "Man");

List<Customer> customers = new List<Customer>();
customers.Add(customerOne);
customers.Add(customerTwo);
customers.Add(customerThree);
customers.Add(customerFour);
customers.Add(customerFive);

什么 LINQ 查询将为具有相同姓氏的所有客户返回一个可枚举值？

结果应包括以下实例之一：John Doe、Jane Doe、Super Man 和 Bat Man

重新表述：“您希望按姓氏对客户列表进行分组，过滤掉具有多个元素的组，然后选择每个组的每个实例”。你几乎可以直接将这句话翻译成 C#：

 customers
    .GroupBy(customer => customer.LastName)
    .Where(sameLastName => sameLastName.Skip(1).Any())
    .SelectMany(customer => customer)

或者使用 LINQ 语法：

var q = from customer in customers
        group customer by customer.LastName into sameLastName
        where sameLastName.Skip(1).Any()
        from customer in sameLastName
        select customer;