Linq Group by复杂对象(例如，对象的列表元素)

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

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

public class Program
{
    public static void Main()
    {
        List<Student> students = new List<Student>
        {
            new Student { Id = 1, Name = "Alice", Age = 20, Class = "A" },
            new Student { Id = 2, Name = "Bob", Age = 21, Class = "B" },
            new Student { Id = 3, Name = "Charlie", Age = 20, Class = "A" },
            new Student { Id = 4, Name = "David", Age = 22, Class = "B" }
        };

        var groupedByClass = students.GroupBy(s => s.Class);

        foreach (var group in groupedByClass)
        {
            Console.WriteLine($"Class: {group.Key}");
            foreach (var student in group)
            {
                Console.WriteLine($"  {student.Name}, {student.Age}");
            }
        }
    }
}

var groupedByClass = students.Where(s => !string.IsNullOrEmpty(s.Class)).GroupBy(s => s.Class);