group by 是linq中的分组功能，能通过给定的字段对数据集进行分组，得到分组后的结果。
基本用法
使用扩展函数GroupBy对数据集合通过给定的字段进行分组，新建一个基于.net6的控制台项目，在program.cs中写如下代码，通过班级将学生进行分组展示（顶级语句 ，从 C# 9 开始，无需在控制台应用程序项目中显式包含 Main 方法。 相反，可以使用顶级语句功能最大程度地减少必须编写的代码。 在这种情况下，编译器将为应用程序生成类和 Main 方法入口点。）：
// See https://aka.ms/new-console-template for more information
List<Student> students = new List<Student>() {
new Student(){Name="1",Classroom="a"},
new Student(){Name="2",Classroom="a"},
new Student(){Name="3",Classroom="b"},
new Student(){Name="4",Classroom="b"}
};
var groupStudents=students.GroupBy(student=>student.Classroom);
foreach(var groupStudent in groupStudents)
{
Console.WriteLine(groupStudent.Key);
foreach(var student in groupStudent)
{
Console.WriteLine($"{student.Name},{student.Classroom}");
}
}
public class Student
{
public string Name { get; set; }
public string Classroom { get; set; }
}
分组求和
统计某同学的总分，参考代码：
代码语言：javascript复制// See https://aka.ms/new-console-template for more information
List<Student> students = new List<Student>() {
new Student(){Name="小明",Classroom="a班",Subjects="数学",Score=100},
new Student(){Name="小彭",Classroom="a班",Subjects="数学",Score=100},
new Student(){Name="小明",Classroom="a班",Subjects="语文",Score=90},
new Student(){Name="小黄",Classroom="b班",Subjects="语文",Score=90}
};
var groupStudents = from student in students
group student by new { student.Name, student.Classroom }
into res
select new Student
{
Name = res.First().Name,
Classroom = res.First().Classroom,
Subjects = "已考科目总分",
Score = res.Sum(x => x.Score),
};
foreach (var groupStudent in groupStudents)
{
Console.WriteLine($"{groupStudent.Name},{groupStudent.Classroom},{groupStudent.Subjects},{groupStudent.Score}");
}
public class Student
{
/// <summary>
/// 姓名
/// </summary>
public string Name { get; set; }
/// <summary>
/// 班级
/// </summary>
public string Classroom { get; set; }
/// <summary>
/// 科目
/// </summary>
public string Subjects { get; set; }
/// <summary>
/// 分数
/// </summary>
public float Score { get; set; }
}
