Linq排序依据，分组依据和各组排序？

我有一个看起来像这样的对象：

public class Student
{
    public string Name { get; set; } 
    public int Grade { get; set; }
}

我想创建以下查询：按学生姓名对成绩进行分组，按成绩对每个学生组进行排序，并按每个组中的最高成绩对组进行排序。

因此它将如下所示：

A 100
A 80
B 80
B 50
B 40
C 70
C 30

我创建了以下查询：

StudentsGrades.GroupBy(student => student.Name)
    .OrderBy(studentGradesGroup => studentGradesGroup.Max(student => student.Grade));

但这返回了IEnumerable IGrouping，并且我无法对列表进行排序，除非在另一个foreach查询中执行此操作，然后使用将结果添加到其他列表中AddRange。

有没有更漂亮的方法可以做到这一点？

当然：

var query = grades.GroupBy(student => student.Name)
                  .Select(group => 
                        new { Name = group.Key,
                              Students = group.OrderByDescending(x => x.Grade) })
                  .OrderBy(group => group.Students.First().Grade);

请注意，您可以在订购后只获得各组中的第一年级，因为您已经知道第一项将是最高分。

然后，您可以显示它们：

foreach (var group in query)
{
    Console.WriteLine("Group: {0}", group.Name);
    foreach (var student in group.Students)
    {
        Console.WriteLine("  {0}", student.Grade);
    }
}

无需投影的方式：

StudentsGrades.OrderBy(student => student.Name).
ThenBy(student => student.Grade);

我认为您需要一个额外的投影，将每个组映射到该组的排序版本：

.Select(group => group.OrderByDescending(student => student.Grade))

这似乎也像你可能想后，另一扁平化操作，这将给你的学生，而不是组序列的序列：

.SelectMany(group => group)

您始终可以将它们折叠成一个单独的 SelectMany调用，以一起进行投影和展平。

编辑：正如乔恩·斯凯特（Jon Skeet）所指出的那样，整个查询中存在某些效率低下的问题；从排序每个组获得的信息未用于组本身的排序。通过将每个组的排序移到组本身的排序之前，Max可以将查询规避为更简单的First查询。

尝试这个...

public class Student 
    {
        public int Grade { get; set; }
        public string Name { get; set; }
        public override string ToString()
        {
            return string.Format("Name{0} : Grade{1}", Name, Grade);
        }
    }

class Program
{
    static void Main(string[] args)
    {

      List<Student> listStudents = new List<Student>();
      listStudents.Add(new Student() { Grade = 10, Name = "Pedro" });
      listStudents.Add(new Student() { Grade = 10, Name = "Luana" });
      listStudents.Add(new Student() { Grade = 10, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 11, Name = "Mario" });
      listStudents.Add(new Student() { Grade = 15, Name = "Mario" });
      listStudents.Add(new Student() { Grade = 10, Name = "Bruno" });
      listStudents.Add(new Student() { Grade = 10, Name = "Luana" });
      listStudents.Add(new Student() { Grade = 11, Name = "Luana" });
      listStudents.Add(new Student() { Grade = 22, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 55, Name = "Bruno" });
      listStudents.Add(new Student() { Grade = 77, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 66, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 88, Name = "Bruno" });
      listStudents.Add(new Student() { Grade = 42, Name = "Pedro" });
      listStudents.Add(new Student() { Grade = 33, Name = "Bruno" });
      listStudents.Add(new Student() { Grade = 33, Name = "Luciana" });
      listStudents.Add(new Student() { Grade = 17, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 25, Name = "Luana" });
      listStudents.Add(new Student() { Grade = 25, Name = "Pedro" });

      listStudents.GroupBy(g => g.Name).OrderBy(g => g.Key).SelectMany(g => g.OrderByDescending(x => x.Grade)).ToList().ForEach(x => Console.WriteLine(x.ToString()));
    }
}

或者，您可以这样做：

     var _items = from a in StudentsGrades
                  group a by a.Name;

     foreach (var _itemGroup in _items)
     {
        foreach (var _item in _itemGroup.OrderBy(a=>a.grade))
        {
           ------------------------
           --------------------------
        }
     }