javascript - 如何在 Javascript 中重新组合对象？

Question

我有一个位置列表:

[
 {
    "id": 1,
    "name": "Location 1",
    "city": {
        "id": 7,
        "name": "Phoenix",
    }
 },
 {
    "id": 2,
    "name": "Location 2",
    "city": {
        "id": 7,
        "name": "Phoenix",
    }
 },
 {
    "id": 3,
    "name": "Location 3",
    "city": {
        "id": 11,
        "name": "Los Angeles",
    }
 }
]

除此之外，我想创建一系列城市，每个城市都有来自该城市的位置。

结果示例:

[
  {
        "id": 7,
        "name": "Phoenix",
        "locations": [
               // location objects from Phoenix (Location 1 and Location 2)
            {
                "id": 1,
                "name": "Location 1",
                "city": {
                  "id": 7,
                  "name": "Phoenix",
                 }
             },
             {
                 "id": 2,
                 "name": "Location 2",
                 "city": {
                    "id": 7,
                    "name": "Phoenix",
                  }
              }
        ]
  },
  {
        "id": 11,
        "name": "Los Angeles",
        "locations": [
               // location objects from Los Angeles (Location 3)
            {
                 "id": 3,
                 "name": "Location 3",
                 "city": {
                    "id": 11,
                    "name": "Los Angeles",
                 }
             }
        ]
   }
]

我尝试使用 .map() 和 .filter() 来获取城市的唯一值数组。它没有为整个city返回唯一、不同的值(return item.city)，所以我只使用了name属性(return item.city.name) 因为我并不真正关心城市 ID。我得到了一系列独特的城市名称:

var cities = data.map(function (item) {
    return item.city.name;
}).filter(function (value, index, self) {
    return self.indexOf(value) === index;
});

现在我一直致力于构建一个数组，该数组将列出位置作为每个城市的属性。预先感谢您...

Answer 1

我首先会创建一个对象，其键设置为城市 ID。然后，如果您需要数组中的这些对象，只需在键上调用 map 即可。例如创建一个以 ID 为键的对象:

var arr = [{"id": 1,"name": "Location 1","city": {"id": 7,"name": "Phoenix",}},{"id": 2,"name": "Location 2","city": {"id": 7,"name": "Phoenix",}},{"id": 3,"name": "Location 3","city": {"id": 11,"name": "Los Angeles",}}]

var obj = arr.reduce((a, c) => {
    if (a[c.city.id]) a[c.city.id].push(c)
    else  a[c.city.id] = [c]
    return a
}, {})

console.log(obj)

现在你有了一个干净的对象，如果你想要一个数组，只需在键上添加一个映射:

var arr = [{"id": 1,"name": "Location 1","city": {"id": 7,"name": "Phoenix",}},{"id": 2,"name": "Location 2","city": {"id": 7,"name": "Phoenix",}},{"id": 3,"name": "Location 3","city": {"id": 11,"name": "Los Angeles",}}]

var obj = arr.reduce((a, c) => {
    if (a[c.city.id]) a[c.city.id].locations.push(c)
    else  a[c.city.id] = {name: c.city.name, locations:[c]}
    return a
}, {})

var arr_version = Object.keys(obj).map(k => Object.assign({id: k}, obj[k]))

console.log(arr_version)