Javascript数组中的联接和聚合

Joins and Aggregates in Javascript Arrays

本文关键字：数组 Javascript      更新时间：2023-09-26

我已经尝试了几个小时使用json.js来完成这项工作，但对于看似简单的事情来说太多了。我有这个示例数据：

    var hotels = [
        { id: 101, Name: "Hotel 101", WebFacilities: [8, 9, 10] },
        { id: 102, Name: "Hotel 101", WebFacilities: [8] },
        { id: 103, Name: "Hotel 101", WebFacilities: [8, 10] }
    ];
    var facilities = [
        { id: 8, Name: "Facility 8" },
        { id: 9, Name: "Facility 9" },
        { id: 10, Name: "Facility 10" }
    ];

我想得到这个：

    var selectedFacilities = [
        { id: 8, Name: "Facility 8", Count: 3 },
        { id: 9, Name: "Facility 9", Count: 1 },
        { id: 10, Name: "Facility 10", Count: 2 }
    ];

我该怎么做？

因此，您似乎正在尝试计算每个设施的数量。

以下是使用C#编写查询的一种方法：

var hotelFacilities =
    from hotel in hotels
    from id in hotel.WebFacilities
    group id by id;
var query =
    from facility in facilities
    join g in hotelFacilities on facility.id equals g.Key
    select new
    {
        id = facility.id,
        Name = facility.Name,
        Count = g.Count(),
    };

现在，如果您可以使用方法语法来描述这一点，那么它几乎是对linq.js版本的1:1转换。

请注意，编译器转换上述内容的方式通常会在前一个SelectMany()调用中包含GroupBy()调用。然而，以这种方式编写将使编写linq.js等效查询变得更容易，也不那么尴尬。

var hotelFacilities = hotels
    .SelectMany(hotel => hotel.WebFacilities)
    .GroupBy(id => id);
var query = facilities
    .Join(
        hotelFacilities,
        facility => facility.id,
        g => g.Key,
        (facility, g) => new
        {
            id = facility.id,
            Name = facility.Name,
            Count = g.Count(),
        }
    );

以及等价的linq.js查询。

var hotelFacilities = Enumerable.From(hotels)
    .SelectMany("hotel => hotel.WebFacilities")
    .GroupBy("id => id")
    .ToArray();
var query = Enumerable.From(facilities)
    .Join(
        hotelFacilities,
        "facility => facility.id",
        "g => g.Key()",
        "(facility, g) => { id: facility.id, Name: facility.Name, Count: g.Count() }"
    ).ToArray();

使用此：

var selectedFacilities = facilities;
for(var i = 0; i < facilities.length; i++) {
    for(var j = 0; j < hotels.length; j++) {
        if(hotels[j]["id"] == facilities[i]["id"]) {
            // Add data
            selectedFacilities[i]["Count"] = hotels[i]["WebFacilities"].length;
        } else {
            selectedFacilities[i]["Count"] = 0;
        }
    }
}
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