按 Linq 多列分组 C#

在 C# 中，使用 Linq 可以轻松地将数据按照一个或多个列进行分组。本文将介绍如何使用 Linq 在 C# 中实现按多列分组。

简单的多列分组

假设我们有以下 Student 类型的对象：

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

我们想要按照年龄和专业分组，可以使用以下 Linq 查询：

var students = new List<Student>
{
    new Student { Name = "Alice", Age = 20, Gender = "Female", Major = "Computer Science" },
    new Student { Name = "Bob", Age = 21, Gender = "Male", Major = "Computer Science" },
    new Student { Name = "Charlie", Age = 20, Gender = "Male", Major = "Mathematics" },
    new Student { Name = "David", Age = 22, Gender = "Male", Major = "Mathematics" },
    new Student { Name = "Emily", Age = 21, Gender = "Female", Major = "Computer Science" }
};

var groupedStudents = from student in students
                      group student by new { student.Age, student.Major };

这将返回一个 IGrouping 对象的集合，每个 IGrouping 对象对应一个分组：

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

    foreach (var student in group)
    {
        Console.WriteLine($"    {student.Name} ({student.Gender})");
    }
}

输出结果为：

Age: 20, Major: Computer Science
    Alice (Female)
    Bob (Male)
Age: 20, Major: Mathematics
    Charlie (Male)
Age: 21, Major: Computer Science
    Emily (Female)
Age: 22, Major: Mathematics
    David (Male)

可以看到，我们成功地按照年龄和专业将学生分组。

自定义多列分组

有时，我们需要使用自定义的函数来分组。例如，我们想要将字符串按照首字母分组，可以使用以下 Linq 查询：

var strings = new List<string> { "apple", "banana", "cat", "dog", "elephant", "fox" };

var groupedStrings = from s in strings
                     group s by s[0] into g
                     orderby g.Key
                     select new { FirstLetter = g.Key, Words = g };

foreach (var group in groupedStrings)
{
    Console.WriteLine($"Words starting with '{group.FirstLetter}':");

    foreach (var word in group.Words)
    {
        Console.WriteLine($"    {word}");
    }
}

这将返回一个匿名类型的对象的集合：

Words starting with 'a':
    apple
Words starting with 'b':
    banana
Words starting with 'c':
    cat
Words starting with 'd':
    dog
Words starting with 'e':
    elephant
Words starting with 'f':
    fox

结论

在 C# 中，使用 Linq 可以轻松地按照一个或多个列进行分组。我们可以使用简单的语法来分组，也可以使用自定义的函数来分组。这些功能使得我们可以更方便地对数据进行处理和分析。