LINQ分组以展平层次结构

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

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

public class Program
{
    public static void Main()
    {
        List<Person> people = new List<Person>
        {
            new Person { Name = "Alice", Age = 30 },
            new Person { Name = "Bob", Age = 25 },
            new Person { Name = "Charlie", Age = 30 },
            new Person { Name = "David", Age = 25 }
        };

        var groupedByAge = people.GroupBy(p => p.Age);

        foreach (var group in groupedByAge)
        {
            Console.WriteLine($"Age: {group.Key}, Count: {group.Count()}");
        }
    }
}

var result = groupedByAge.Select(g => new
{
    Age = g.Key,
    AverageNameLength = g.Average(p => p.Name.Length),
    OldestPerson = g.OrderByDescending(p => p.Name.Length).First()
});

foreach (var item in result)
{
    Console.WriteLine($"Age: {item.Age}, Avg Name Length: {item.AverageNameLength}, Oldest Person: {item.OldestPerson.Name}");
}