Question

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：按学生姓名分组成绩，按成绩对每个学生组进行排序，并按每组中的最高成绩订购组。

所以它看起来像这样：

我创建了以下查询：

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

但是返回IEnumerable IGrouping，我无法对列表进行排序，除非我在另一个foreach查询中执行此操作，并使用{将结果添加到其他列表{1}}。

有更好的方法吗？

Answer 1

不确定

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，您可以在订购后取得每组中的一年级，因为您已经知道第一个参赛作品的成绩最高。

然后你可以用以下方式显示它们：

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

Answer 2

没有投影的方法：

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

Answer 3

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))

看起来你可能希望在此之后再进行另一次展平操作，这会给你一系列学生而不是一系列的小组：

.SelectMany(group => group)

您可以随时将两者都折叠为一起执行投影和展平的单 SelectMany调用。

编辑：正如Jon Skeet指出的那样，整体查询存在一些效率低下的问题;从排序每个组中获得的信息不会用于组本身的排序。通过将每个组的排序移动到之前组本身的排序，Max查询可以被转移到更简单的First查询中。

Answer 4

试试这个......

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()));
    }
}

Answer 5

或者你可以这样做：

     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))
        {
           ------------------------
           --------------------------
        }
     }

Linq按顺序分组，每组按顺序排序？

5 个答案: