使用LINQ過濾串列-有解無憂

我有，列出Students并Teachers

var students = new List<Student>
    {
        new Student
        {
            Id= 1,
            Name = "AA",
            City = "London",
            Country = "UK"
        },
        new Student
        {
            Id= 2,
            Name = "BB",
            City = "New Orleans",
            Country = "USA"
        }
    }

var teachers = new List<Teacher>
    {
        new Teacher
        {
            Id = 1,
            Name = "CC",
            City = "Berlin",
            Country = "Germany"
        },
        new Teacher
        {
            Id = 2,
            Name = "DD",
            City = "Mexico D.F.",
            Country = "Mexico"
        }
    }

我想為每位老師獲取位于同一個國家和同一個城市的學生名單。

到目前為止我做了什么：

var result = from teacher in teachers
                     select new
                     {
                         teacher,
                         Students = students.Where(s => s.Country == teacher.Country && s.City == teacher.City).ToList()
                     };

這不起作用，我得到了casting exception。并嘗試：

var result = new List<(Teacher, IEnumerable<Student>)>();

teachers.ToList().ForEach(c => result.Add((c,
        students.Where(s => s.Country == c.Country && s.City == c.City).ToList())));

這作業得很好，但是，有沒有其他方法而不回圈？

uj5u.com熱心網友回復：

您的 linq 查詢是正確的。您的查詢回傳匿名型別的串列。您不能將其直接轉換為元組串列。您遇到的問題是您要轉換為哪種型別。如果你想得到像 IEnumerable<(Teacher, IEnumerable)> 這樣的元組串列的結果，你應該編碼如下：

        var result = from teacher in teachers
                     select (
                         teacher,
                         students.Where(s => s.Country == teacher.Country && s.City == teacher.City).ToList()
                         );

然后， result.ToList() 會給你一個元組串列， result.ToArray() 會給你一個元組陣列

Lambda 運算式替代：

var result = teachers
            .Select(teacher => (teacher, students.Where(s => s.Country == teacher.Country && s.City == teacher.City).ToList()));

但是，我更喜歡匿名串列作為回傳型別而不是元組。

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標籤：C＃列表林克泛型拉姆达

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