示例1：
GroupBy 分组在List<>泛型中的应用
原表：
按姓名Nam 分组后结果：
对DATATABLE 进行LAMDA查询时必须在项目的引用中添加 System.Data.DataSetExtensions
代码：
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
List<Person> persons1 = new List<Person>();
private void Form1_Load(object sender, EventArgs e)
{
initForm();
}
private void initForm()
{//窗体初始化
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));
dataGridView1.DataSource = persons1;
}
private void button1_Click(object sender, EventArgs e)
{
//******* 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) };
dataGridView1.DataSource = ls.ToList();
//dataGridView1.DataSource = ls2.ToList();
}
}
/// <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;
}
}