在LINQ中,分组运算符选择包含公共属性的序列或集合的元素,然后将它们作为一个组来提供服务。换句话说,我们可以说分组运算符基于给定的键返回元素组。该组保存在一种特殊的集合中,该集合实现IGrouping
标准查询运算符包含两种不同类型的分组运算符:
- 通过…分组
- 去查查看
ToLookup运算子
ToLookup运算符用于根据键选择器函数将元素放入LookUp
重要事项:
- 它不支持C#和VB.Net语言的查询语法。
- 它支持C#和VB.Net语言的方法语法。
- 它仅存在于Enumerable类中。
- 它有四种不同类型的重载。
- 如果source或keySelector为null,则抛出ArgumentNullException。
- 通过使用立即执行来实现。
例子:
// C# program to divide the employees in
// groups according to their gender
using System;
using System.Linq;
using System.Collections.Generic;
// Employee details
public class Employee {
public int emp_id
{
get;
set;
}
public string emp_name
{
get;
set;
}
public string emp_gender
{
get;
set;
}
public string emp_hire_date
{
get;
set;
}
public int emp_salary
{
get;
set;
}
}
class GFG {
// Main method
static public void Main()
{
List emp = new List() {
new Employee() {emp_id = 209, emp_name = "Anjita", emp_gender = "Female",
emp_hire_date = "12/3/2017", emp_salary = 20000},
new Employee() {emp_id = 210, emp_name = "Soniya", emp_gender = "Female",
emp_hire_date = "22/4/2018", emp_salary = 30000},
new Employee() {emp_id = 211, emp_name = "Rohit", emp_gender = "Male",
emp_hire_date = "3/5/2016", emp_salary = 40000},
new Employee() {emp_id = 212, emp_name = "Supriya", emp_gender = "Female",
emp_hire_date = "4/8/2017", emp_salary = 40000},
new Employee() {emp_id = 213, emp_name = "Anil", emp_gender = "Male",
emp_hire_date = "12/1/2016", emp_salary = 40000},
new Employee() {emp_id = 214, emp_name = "Anju", emp_gender = "Female",
emp_hire_date = "17/6/2015", emp_salary = 50000},
};
// Query to divide the employees
// in the groups according to
// their gender Using the
// ToLookup method
var res = emp.ToLookup(e => e.emp_gender);
foreach(var val in res)
{
// Here salary is the key value
Console.WriteLine("Group By Gender: {0}", val.Key);
// Display name of the employees
foreach(Employee e in val)
{
Console.WriteLine("Employee Name: {0}", e.emp_name);
}
}
}
}
输出:
Group By Gender: Female
Employee Name: Anjita
Employee Name: Soniya
Employee Name: Supriya
Employee Name: Anju
Group By Gender: Male
Employee Name: Rohit
Employee Name: Anil