C# Linq查本集合中不包含于另一个集合的元素

public void Linq() {
    List<Product> products = GetProductList();
    List<Customer> customers = GetCustomerList();

    var productFirstChars =
        from prod in products
        select prod.ProductName[0];
    var customerFirstChars =
        from cust in customers
        select cust.CompanyName[0];

    var productOnlyFirstChars = productFirstChars.Except(customerFirstChars);  

　　//筛选表所有修改的数据（差集）(同样适用于DataTable)

　　//DataTable    dtResult = dtAllData.AsEnumerable().Except(dtPartData.AsEnumerable());

 Console.WriteLine("First letters from Product names, but not from Customer names:"); foreach (var ch in productOnlyFirstChars) { Console.WriteLine(ch); } }