使用LINQ如何通过"计算字段"进行分组

using System;
using System.Collections.Generic;
using System.Linq;

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

class Program
{
    static void Main(string[] args)
    {
        List<Student> students = new List<Student>
        {
            new Student { Name = "Tom", Age = 18 },
            new Student { Name = "Jerry", Age = 20 },
            new Student { Name = "Alice", Age = 19 },
            new Student { Name = "Bob", Age = 21 },
            new Student { Name = "Cathy", Age = 22 }
        };

        var result = students.GroupBy(s => GetAgeGroup(s.Age))
                            .Select(g => new
                            {
                                AgeGroup = g.Key,
                                AverageAge = g.Average(s => s.Age)
                            });

        foreach (var item in result)
        {
            Console.WriteLine($"Age group: {item.AgeGroup}, Average age: {item.AverageAge}");
        }
    }

    static string GetAgeGroup(int age)
    {
        if (age < 20)
        {
            return "Under 20";
        }
        else if (age < 25)
        {
            return "20-24";
        }
        else
        {
            return "Over 25";
        }
    }
}