C# Linq在Group By内部创建派生类列表

var students = new List<Student>
{
    new Student { Name = "Alice", Age = 20, Grade = "A" },
    new Student { Name = "Bob", Age = 21, Grade = "B" },
    new Student { Name = "Charlie", Age = 20, Grade = "A" },
    new Student { Name = "David", Age = 22, Grade = "C" },
    new Student { Name = "Eve", Age = 21, Grade = "B" }
};

var groupedStudents = students.GroupBy(s => s.Grade)
                              .Select(g => new GradeSummary
                              {
                                  Grade = g.Key,
                                  Count = g.Count(),
                                  AverageAge = g.Average(s => s.Age)
                              });

foreach (var summary in groupedStudents)
{
    Console.WriteLine($"Grade: {summary.Grade}, Count: {summary.Count}, Average Age: {summary.AverageAge}");
}

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

public class GradeSummary
{
    public string Grade { get; set; }
    public int Count { get; set; }
    public double AverageAge { get; set; }
}