c# Linq及Lamda表达式应用经验之 GroupBy 分组

对DATATABLE 进行LAMDA查询时必须在项目的引用中添加 System.Data.DataSetExtensions 

1 手动设计一个Person类

/// <summary>  
/// 手动设计一个Person类。用于放到List泛型中  
/// </summary>  
public class Person  
{  
     public string Name { get; set; }  
     public int Age  { get;private set; }  
     public string Sex { get; set; }  
     public int Money { get; set; }  
      
      public Person(string name, string sex, int age, int money)  
      {  
            Name = name;  
            Age = age;  
            Sex = sex;  
            Money = money;  
       } 
}

2 填充数据

List<Person> persons1 = new List<Person>();  

persons1.Add(new Person("张三", "男", 20, 1500));  
persons1.Add(new Person("王成", "男", 32, 3200));  
persons1.Add(new Person("李丽", "女", 19, 1700));  
persons1.Add(new Person("何英", "女", 35, 3600));  
persons1.Add(new Person("何英", "女", 18, 1600));  

3 分组

//******* 对集合按Name属于进行分组GroupBy查询 ********  
//结果中包括的字段：  
//1、分组的关键字：Name = g.Key  
//2、每个分组的数量：count = g.Count()  
//3、每个分组的年龄总和：ageC = g.Sum(item => item.Age)  
//4、每个分组的收入总和：moneyC = g.Sum(item => item.Money)  
      
//写法1：lamda 表达式写法（推荐）  
var ls = persons1.GroupBy(a => a.Name).Select(g => (new { name = g.Key, count = g.Count(), ageC = g.Sum(item => item.Age), moneyC = g.Sum(item => item.Money) }));  
//写法2：类SQL语言写法 最终编译器会把它转化为lamda表达式  
var ls2 = from ps in persons1  
              group ps by ps.Name  
              into g  
              select new { name = g.Key, count = g.Count(), ageC = g.Sum(item => item.Age), moneyC = g.Sum(item => item.Money) };