c# linq goup by实例

using System;
using System.Collections.Generic;
using System.Linq;namespace ConsoleApp3
{class Program{static void Main(string[] args){List<Student> Students = GetStudents();//group by 一个字段var query1 = from a in Studentsgroup a by a.SchoolID into bselect new{SchoolID = b.Key,Count = b.Count()};//group by 多个字段var query2 = from a in Studentsgroup a by new { SchoolID = a.SchoolID, SchoolName = a.SchoolName } into bselect new{SchoolID = b.Key.SchoolID,SchoolName = b.Key.SchoolName,Count = b.Count()};//group by 能获取子集合var query3 = Students.GroupBy(a => new { SchoolID = a.SchoolID, SchoolName = a.SchoolName });if (query3.Count() > 0){foreach (var item in query3){int SchoolID = item.Key.SchoolID;string SchoolName = item.Key.SchoolName;List<Student> list = item.ToList();}}}private static List<Student> GetStudents(){List<Student> students = new List<Student>();students.Add(new Student(1, "student1", 1, "学校1"));students.Add(new Student(2, "student2", 1, "学校1"));students.Add(new Student(3, "student3", 2, "学校2"));students.Add(new Student(4, "student4", 2, "学校2"));students.Add(new Student(5, "student5", 3, "学校3"));return students;}}public class Student{public Student() { }public Student(int _studentID, string _studentName, int _schoolID, string _schoolName){this.StudentID = _studentID;this.StudentName = _studentName;this.SchoolID = _schoolID;this.SchoolName = _schoolName;}public int StudentID { get; set; }public string StudentName { get; set; }public int SchoolID { get; set; }public string SchoolName { get; set; }}
}

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