Linq 中, GroupBy 之后 OrderBy
GroupBy().OrderBy() 是对 Key 进行的排序，所以想要对每组内的 Value 进行排序，需要 Foreach 之内对每个 Group 进行 OrderBy。
代码示例
```csharp using System; using System.Collections.Generic; using System.Linq;namespace ConsoleApplication1
{
internal class Program
{
static DateTime ParseDate(string date)
{
DateTime.TryParse(date, out var d);
return d;
}
public static void Main(string[] args)
{
var students = new List<Student>
{
new Student { Info = new Info(){Name = "Alice", Score = 90, Date = ParseDate("9/14/2023 10:10:00 AM")}},
new Student { Info = new Info(){Name = "Bob", Score = 85 , Date = ParseDate("9/14/2023 10:20:00 AM")}},
new Student { Info = new Info(){Name = "Charlie", Score = 95 , Date = ParseDate("9/14/2023 10:12:00 AM")}},
new Student { Info = new Info(){Name = "David", Score = 85 , Date = ParseDate("9/14/2023 10:13:00 AM")}},
new Student { Info = new Info(){Name = "Kiz", Score = 85 , Date = ParseDate("9/14/2023 10:30:00 AM")}},
new Student { Info = new Info(){Name = "Eve", Score = 92 , Date = ParseDate("9/14/2023 10:16:00 AM")}}
};
// 使用 GroupBy() 方法按分数分组
var groupedStudents = students.GroupBy(student => student.Info.Score);
// 对每个分组内的学生按分数降序排序，<b>这个结果只是在分组的排序，不是每个组内的排序</b>
var sortedGroups = groupedStudents.OrderByDescending(group => group.Key);
// 输出结果
Console.WriteLine($"不对结果进行时间排序：");
foreach (var group in sortedGroups.Where(t=>t.Key.Equals(85)))
{
Console.WriteLine($"分数: {group.Key}");
foreach (var student in group)
{
var info = student.Info;
Console.WriteLine($" 学生姓名: {info.Name}, {info.Score}, {info.Date}");
}
}
// output:
// 不对结果进行时间排序：
// 分数: 85
// 学生姓名: Bob, 85, 9/14/2023 10:20:00 AM
// 学生姓名: David, 85, 9/14/2023 10:13:00 AM
// 学生姓名: Kiz, 85, 9/14/2023 10:30:00 AM
Console.WriteLine($"{Environment.NewLine}对结果进行时间排序：");
foreach (var group in sortedGroups.Where(t=>t.Key.Equals(85)))
{
Console.WriteLine($"分数: {group.Key}");
foreach (var student in group.OrderByDescending(t => t.Info.Date))
{
var info = student.Info;
Console.WriteLine($" 学生姓名: {info.Name}, {info.Score}, {info.Date}");
}
}
// output:
// 对结果进行时间排序：
// 分数: 85
// 学生姓名: Kiz, 85, 9/14/2023 10:30:00 AM
// 学生姓名: Bob, 85, 9/14/2023 10:20:00 AM
// 学生姓名: David, 85, 9/14/2023 10:13:00 AM
}
}
public class Student
{
public Info Info { get; set; }
}
public class Info
{
public string Name { get; set; }
public int Score { get; set; }
public DateTime Date { get; set; }
}
}
</details>