如何使用 linq 将列表中的列表转换为单个列表 [重复]

Posted 2023-03-31

【中文标题】如何使用 linq 将列表中的列表转换为单个列表 [重复]

【英文标题】：How to translate a list inside of a list to a single list with linq [duplicate]

【发布时间】：2018-07-12 14:32:19

【问题描述】：

如果我有如下对象：

public class Teacher

    public int TeacherId  get; set; 
    public string TeacherName  get; set; 
    public List<string> StudentNames  get; set; 

我想将其翻译成一个列表，其中每个教师姓名与每个学生姓名配对。

public class TeacherStudent


    public int TeacherId  get; set; 
    public string TeacherName  get; set; 
    public string StudentName  get; set; 

我知道我可以通过这样的循环来做到这一点：

var teachers = new List<Teacher>();
teachers.Add(new Teacher()  TeacherId = 1, TeacherName = "Teacher1", StudentNames = new List<string>()  "Student1", "Student2"  );
teachers.Add(new Teacher()  TeacherId = 2, TeacherName = "Teacher2", StudentNames = new List<string>()  "Student3", "Student4", "Student5"  );
teachers.Add(new Teacher()  TeacherId = 3, TeacherName = "Teacher3", StudentNames = new List<string>()  "Student6", "Student7"  );


var teacherStudents = new List<TeacherStudent>();
foreach(var teacher in teachers)


    foreach (var studentName in teacher.StudentNames)
    
        teacherStudents.Add(new TeacherStudent()  TeacherId = teacher.TeacherId, TeacherName = teacher.TeacherName, StudentName = studentName );
    

似乎应该有一种方法可以用 linq 做到这一点，但我无法弄清楚。

【问题讨论】：

一个学生可以有多位老师吗？例如Student1 出现在Teacher1 和Teacher2 上？

【参考方案1】：

你可以使用SelectMany:

teachers.SelectMany(t =>
            t.StudentNames.Select(s => new TeacherStudent
            
                TeacherId = t.TeacherId,
                TeacherName = t.TeacherName,
                StudentName = s
            ));