使用GroupBy和Select的c# Linq方法

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

public class Program
{
    public static void Main()
    {
        // 创建一个包含学生信息的集合
        List<Student> students = new List<Student>()
        {
            new Student { Name = "Alice", Age = 18, Grade = "A" },
            new Student { Name = "Bob", Age = 19, Grade = "B" },
            new Student { Name = "Charlie", Age = 18, Grade = "A" },
            new Student { Name = "David", Age = 19, Grade = "C" },
            new Student { Name = "Eve", Age = 18, Grade = "B" }
        };

        // 使用GroupBy方法按年龄进行分组
        var groupedByAge = students.GroupBy(s => s.Age);

        // 使用Select方法对每个分组进行投影，获取每个分组的平均年龄和学生数量
        var result = groupedByAge.Select(g => new
        {
            AverageAge = g.Average(s => s.Age),
            StudentCount = g.Count()
        });

        // 打印结果
        foreach (var group in result)
        {
            Console.WriteLine($"Average Age: {group.AverageAge}, Student Count: {group.StudentCount}");
        }
    }
}

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