javascript - 如何在 JavaScript 中以类似于 LINQ 的方式进行分组和求和

Question

我对此感到疯狂。也许你可以帮忙。

假设有以下 .NET 类:

老师:

public class Teacher
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public Class[] Classes { get; set; }
}

类别

public class Class
{
    public int Id { get; set; }
    public string Name { get; set; }
    public Attendee[] Attendees { get; set; }
}

与会者

public class Attendee
{
 public int Id { get; set; }
 public string FirstName { get; set; }
 public string LastName { get; set; }
 public int Presences { get; set; }
}

根据这个结构我们以如下数据为例:

var teachers = 
    new Teacher[] {
        new Teacher{ Id = 1, FirstName="Michael", LastName = "Knight",
            Classes = new Class[]{
                new Class{ Id = 1, Name = "Maths",
                    Attendees = new Attendee[]{
                        new Attendee{ Id = 1, FirstName = "Templeton", LastName = "Peck", Presences=22 },
                        new Attendee{ Id = 2, FirstName = "Stringfellow", LastName = "Hawke", Presences=20 }
                    }
                },
                new Class{ Id = 1, Name = "English",
                    Attendees = new Attendee[]{
                        new Attendee{ Id = 3, FirstName = "Morris", LastName = "Buttermaker", Presences=25 },
                        new Attendee{ Id = 4, FirstName = "Ben", LastName = "Matlock", Presences=18 },
                        new Attendee{ Id = 5, FirstName = "Kelly", LastName = "Taylor", Presences=22 },
                        new Attendee{ Id = 5, FirstName = "Marty", LastName = "McFly", Presences=0 }
                    }
                }
            }
        },
        new Teacher{ Id = 2, FirstName="Murray", LastName = "Bozinsky",
            Classes = new Class[]{
                new Class{ Id = 1, Name = "Maths",
                    Attendees = new Attendee[]{
                        new Attendee{ Id = 6, FirstName = "Luke", LastName = "Duke", Presences=21 },
                        new Attendee{ Id = 7, FirstName = "Bo", LastName = "Darville", Presences=26 },
                        new Attendee{ Id = 8, FirstName = "Frank", LastName = "Columbo", Presences=20 }
                    }
                },
                new Class{ Id = 1, Name = "English",
                    Attendees = new Attendee[]{
                        new Attendee{ Id = 9, FirstName = "Philip", LastName = "Banks", Presences=28 },
                        new Attendee{ Id = 10, FirstName = "Lynn", LastName = "Tanner", Presences=18 }
                    }
                }
            }
        }
    };

我现在想做的是总结所有出席的教师。在 LINQ 中我会这样做:

var result = teachers
    .Select(p => 
        new { 
            TeacherFirstName = p.FirstName, 
            TeacherLastName = p.LastName, 
            Presences = p.Classes
                .SelectMany(q => q.Attendees.Select(r => r.Presences))
                .Sum() });

这给了我(作为 JSON):

[
    {"TeacherFirstName":"Michael","TeacherLastName":"Knight","Presences":107}, 
    {"TeacherFirstName":"Murray","TeacherLastName":"Bozinsky","Presences":113}
]

如何使用 JavaScript 获取以下 JSON 对象来执行此操作:

[
    {
        "Id":1,"FirstName":"Michael","LastName":"Knight",
        "Classes":
        [
            {
                "Id":1,"Name":"Maths",
                "Attendees":
                [
                    {"Id":1,"FirstName":"Templeton","LastName":"Peck","Presences":22}, 
                    {"Id":2,"FirstName":"Stringfellow","LastName":"Hawke","Presences":20}
                ]
            }, 
            {
                "Id":1,"Name":"English",
                "Attendees":
                [
                    {"Id":3,"FirstName":"Morris","LastName":"Buttermaker","Presences":25}, 
                    {"Id":4,"FirstName":"Ben","LastName":"Matlock","Presences":18}, 
                    {"Id":5,"FirstName":"Kelly","LastName":"Taylor","Presences":22}, 
                    {"Id":5,"FirstName":"Marty","LastName":"McFly","Presences":0}
                ]
            }
        ]
    }, 
    {
        "Id":2,"FirstName":"Murray","LastName":"Bozinsky",
        "Classes":
        [
            {
                "Id":1,"Name":"Maths",
                "Attendees":
                [
                    {"Id":6,"FirstName":"Luke","LastName":"Duke","Presences":21},
                    {"Id":7,"FirstName":"Bo","LastName":"Darville","Presences":26},
                    {"Id":8,"FirstName":"Frank","LastName":"Columbo","Presences":20}
                ]
            },
            {
                "Id":1,"Name":"English",
                "Attendees":
                [
                    {"Id":9,"FirstName":"Philip","LastName":"Banks","Presences":28}, 
                    {"Id":10,"FirstName":"Lynn","LastName":"Tanner","Presences":18}
                ]
            }
        ]
    }
]

我正在玩reduce和map。但我就是无法让它发挥作用。您是否有提示，如何在一个(或两个，或三个，...)衬里中完成此操作？

提前谢谢您。

Answer 1

与 LINQ对于 Javascript，您可以使用几乎相同的代码来获得求和结果。

var teachers = [{ Id: 1, FirstName: "Michael", LastName: "Knight", Classes: [{ Id: 1, Name: "Maths", Attendees: [{ Id: 1, FirstName: "Templeton", LastName: "Peck", Presences: 22 }, { Id: 2, FirstName: "Stringfellow", LastName: "Hawke", Presences: 20 }] }, { Id: 1, Name: "English", Attendees: [{ Id: 3, FirstName: "Morris", LastName: "Buttermaker", Presences: 25 }, { Id: 4, FirstName: "Ben", LastName: "Matlock", Presences: 18 }, { Id: 5, FirstName: "Kelly", LastName: "Taylor", Presences: 22 }, { Id: 5, FirstName: "Marty", LastName: "McFly", Presences: 0 }] }] }, { Id: 2, FirstName: "Murray", LastName: "Bozinsky", Classes: [{ Id: 1, Name: "Maths", Attendees: [{ Id: 6, FirstName: "Luke", LastName: "Duke", Presences: 21 }, { Id: 7, FirstName: "Bo", LastName: "Darville", Presences: 26 }, { Id: 8, FirstName: "Frank", LastName: "Columbo", Presences: 20 }] }, { Id: 1, Name: "English", Attendees: [{ Id: 9, FirstName: "Philip", LastName: "Banks", Presences: 28 }, { Id: 10, FirstName: "Lynn", LastName: "Tanner", Presences: 18 }] }] }],
    result = Enumerable.From(teachers)
        .Select(p => ({
            TeacherFirstName: p.FirstName,
            TeacherLastName: p.LastName,
            Presences: Enumerable.From(p.Classes)
                .SelectMany(q => Enumerable.From(q.Attendees).Select('$.Presences'))
                .Sum()
        }))
        .ToArray();

console.log(result);

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