分组操作

分组是指将数据放入组中的操作，以便每个组中的元素共享一个公共属性。

GroupBy

分享共享公共属性的元素。

方法语法

// GroupBy

class Order
{
    public string Customer { get; set; }
    public string Description { get; set; }
}
...

var orders = new Order[] 
{
    new Order { Customer = "C1", Description = "O1" },
    new Order { Customer = "C2", Description = "O2" },
    new Order { Customer = "C3", Description = "O3" },
    new Order { Customer = "C1", Description = "O4" },
    new Order { Customer = "C1", Description = "O5" },
    new Order { Customer = "C3", Description = "O6" },
};

var groups = orders.GroupBy(o => o.Customer);

// groups: { (Key="C1", Values="O1","O4","O5"), (Key="C2", Values="O2"), (Key="C3", Values="O3","O6") }

查询语法

// group … by

var groups = from o in orders
             group o by o.Customer;

// groups: { (Key="C1", Values="O1","O4","O5"), (Key="C2", Values="O2"), (Key="C3", Values="O3","O6") }

去查查看

基于键选择器函数将元素插入到一对多字典中。

方法语法

// ToLookUp

var ordersByCustomer = orders.ToLookup(o => o.Customer);

// ordersByCustomer = ILookUp<string, Order>
// {
//     "C1" => { Order("01"), Order("04"), Order("05") },
//     "C2" => { Order("02") },
//     "C3" => { Order("03"), Order("06") }
// }

查询语法

// Not applicable.