使用 Linq 对组内的学生进行排序，然后重新排列组顺序

Question

我想要-

• 在每个组中按升序对学生进行排序（例如：第 1 组中的 Jack、John 和 Peter 等）
• 按第一项升序排列所有已排序的组（例如：第 3、2 和 1 组）

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public class StudentInfo
{
  public string Student { get; set; }
  public string University { get; set; }
  public int GroupID { get; set; }
  public bool IsQualified {get; set;}
}

List<StudentInfo> studentsList = new List<StudentInfo>();

StudentsList.Add( new StudentInfo { Student="John", University="ABC", GroupID = 1, IsQualified=False});
StudentsList.Add( new StudentInfo { Student="Jack", University="DEF", GroupID = 1, IsQualified=False} );
StudentsList.Add( new StudentInfo { Student="Peter", University="GHI", GroupID = 1, IsQualified=False} );

StudentsList.Add( new StudentInfo { Student="Olivia", University="ABC", GroupID = 2, IsQualified=False} );
StudentsList.Add( new StudentInfo { Student="Donald", University="JKL", GroupID = 2, IsQualified=False} );

StudentsList.Add( new StudentInfo { Student="Adam", University="GHI", GroupID = 3, IsQualified=False} );
StudentsList.Add( new StudentInfo { Student="Jacob", University="ABC", GroupID = 3, IsQualified=False} );

预期输出

Group 3:
Adam
Jacob

Group 2:
Donald
Olivia

Group 1:
Jack
John
Peter

伪代码

var results = studentsList
 .GroupBy(x => x.GroupID)
 .SelectMany(g => g.OrderBy(x => x.Student)).ToList();

我不知道除此之外还能写什么。请帮帮我。

Answer 1

所以 Linq 查询已经为您排序了数据，但现在您需要显示它。我已经测试过了，它显示了您的预期输出。代码如下：

  static void Main(string[] args)
    {

        List<StudentInfo> studentsList = new List<StudentInfo>();

        studentsList.Add(new StudentInfo { Student = "John", University = "ABC", GroupID = 1, IsQualified = false });
        studentsList.Add(new StudentInfo { Student = "Jack", University = "DEF", GroupID = 1, IsQualified = false });
        studentsList.Add(new StudentInfo { Student = "Peter", University = "GHI", GroupID = 1, IsQualified = false });
        studentsList.Add(new StudentInfo { Student = "Olivia", University = "ABC", GroupID = 2, IsQualified = false });
        studentsList.Add(new StudentInfo { Student = "Donald", University = "JKL", GroupID = 2, IsQualified = false });
        studentsList.Add(new StudentInfo { Student = "Adam", University = "GHI", GroupID = 3, IsQualified = false });
        studentsList.Add(new StudentInfo { Student = "Jacob", University = "ABC", GroupID = 3, IsQualified = false });

        var results = studentsList.OrderBy(x => x.Student)
            .GroupBy(x => x.GroupID);


        foreach (var group in results)
        {
            Console.WriteLine(group.Key);

            foreach (var student in group)
            {
                Console.WriteLine(student.Student);

            }

            Console.WriteLine(Environment.NewLine);
        }
    }

public class StudentInfo
{
    public string Student { get; set; }
    public string University { get; set; }
    public int GroupID { get; set; }
    public bool IsQualified { get; set; }
}

Answer 2

 var groupedStudents = studentsList.GroupBy(a => a.GroupID, (key, Students) => new
 {
     Key = key,
     StudentsList = Students.ToList()
 }).OrderByDescending(a => a.Key).ToList();
 foreach (var item in groupedStudents)
 {
     Console.WriteLine("Group " + item.Key + ":");
     foreach (var stdList in item.StudentsList.OrderBy(a => a.Student))
     {
         Console.WriteLine(stdList.Student);
     }
     Console.WriteLine();
 }

输出：

Group 3:
Adam
Jacob

Group 2:
Donald
Olivia

Group 1:
Jack
John
Peter

Answer 3

根据 Krish 评论更新：

按第一项升序排列所有已排序的组

var results = StudentsList
    .OrderBy(x => x.Student)
    .GroupBy(x => x.GroupID)
    .SelectMany(x => x.OrderBy(y => y.Student))
    .ToList();

根据 YoKidYo 评论更新

var results = StudentsList
     .GroupBy(x => x.GroupID)
     .OrderByDescending(x => x.Key)
     .SelectMany(x => x.OrderBy(y => y.Student))
     .ToList();

foreach (var item in results)
{
    Console.WriteLine(item.GroupID + " : " + item.Student);
}

结果：

3 : Adam
3 : Jacob
2 : Donal
2 : Olivi
1 : Jack
1 : John
1 : Peter

旧代码

您可以按降序Keys(groupId) 排序，并按升序每个组内的学生姓名排序，如以下代码：

var results = StudentsList
     .GroupBy(x => x.GroupID)
     .OrderByDescending(x => x.Key)
     .Select(x => new { Group = "Group " + x.Key, Students = x.Select(y => y.Student).OrderBy(z => z).ToList() })
     .ToList();

希望对你有所帮助。