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) };