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C#高级语法：Linq中使用SelectMany解决列表子项提取、双重for循环的问题

news 来源：原创 2025/6/18 8:27:31

一、列表子项提取

class Program
{
    static void Main()
    {
        var students = new List<Student>
        {
            new Student { Name = "Alice", Courses = new List<string> { "Math", "Science" } },
            new Student { Name = "Bob", Courses = new List<string> { "English", "History" } },
            new Student { Name = "Charlie", Courses = new List<string> { "Art", "Music" } }
        };
 
        //注意：x.Courses的类型是List<string>，SelectMany提取后的结果类型不变，一样是List<string>
        List<string> course_list = students.SelectMany(x => x.Courses).ToList();//["Math", "Science", "English", "History", "Art", "Music"]

    }
}

二、双重for循环

class Program
{
    static void Main()
    {
        var students = new List<string> { "Alice", "Bob", "Charlie" };
        var grades = new List<int> { 90, 80, 85 };

        //x是students的子项，y是grades的子项，第二入参是x和y，出参可以自定义类型
        var result = students.SelectMany(x => grades, (x, y) => new { Name = x, Score = y });// 主列表.SelectMany(x => 次列表, 入参为x和y出参可自定义的委托)

        foreach (var item in result)
        {
            Console.WriteLine($"{item.Name} ：{item.Score}");
        }
        /*
                Alice ：90
                Alice ：80
                Alice ：85
                Bob ：90
                Bob ：80
                Bob ：85
                Charlie ：90
                Charlie ：80
                Charlie ：85
         */
    }
}