Linq按多列对记录进行分组，并选择第一条记录或默认记录

// 假设有一个包含学生信息的对象集合
List<Student> students = new List<Student>
{
    new Student { Name = "Alice", Grade = "A", Age = 18 },
    new Student { Name = "Bob", Grade = "B", Age = 17 },
    new Student { Name = "Alice", Grade = "A", Age = 20 },
    new Student { Name = "Bob", Grade = "C", Age = 19 },
    new Student { Name = "Alice", Grade = "B", Age = 21 }
};

// 使用Linq按Name和Grade列进行分组，并选择每个分组中的第一条记录
var result = students.GroupBy(s => new { s.Name, s.Grade })
                     .Select(g => g.First());

// 输出结果
foreach (var student in result)
{
    Console.WriteLine($"Name: {student.Name}, Grade: {student.Grade}, Age: {student.Age}");
}