根據數組對象列表操作對象進行分組

Question

我正在嘗試找到一種方法來根據組數組轉換此對象列表。 我發現的棘手部分是遍歷組 Array 並將對象應用於多個位置（如果有多個組）。

我也試圖忽略任何不屬於任何事物的群體。 我試過使用 reduce 函數，但無法通過組數組進行迭代。

  let cars = 
    [
      {
        "group":[],
        "name": "All Makes",
        "code": ""
      },
      {
        "group":["Group A"],
        "name": "BMW",
        "code": "X821"
      },
      {
        "group":["Group B"],
        "name": "Audi",
        "code": "B216"
      },
      {
        "group":["Group B"],
        "name": "Ford",
        "code": "P385"    
      },
      {
        "group":["Group B", "Group C"],
        "name": "Mercedes",
        "code": "H801"
      },
      {
        "group":["Group C"],
        "name": "Honda",
        "code": "C213"
      }
    ]

變成這樣：

[
    {
      "group": "Group A",
      "cars": [
         {
           name: "BMW",
           code: "X821"
         }
      ]
    },
    {
      "group": "Group B",
      "cars": [
         {
           name: "Audi",
           code: "B216"
         },
         {
           name: "Ford",
           code: "P385"
         },
         {
           name: "Mercedes",
           code: "H801"
         }
      ]
    },
    {
      "group": "Group C",
      "cars": [
         {
           name: "Mercedes",
           code: "H801"
         },
         {
           name: "Honda",
           code: "C213"
         }
      ]
    }

]

我已經嘗試使用 reduce 來實現這一點，但它並沒有完全達到預期的效果。

const res = cars.reduce((acc, {group, ...r}) => {
  group.forEach(key => {
    acc[key] = (acc[key] || []).concat({...r}); 
  });
  return acc;
}, []);
console.log(res);

Answer 1

在數組上使用字符串鍵不能很好地工作，這就是對象的用途，然后使用Object.values從中獲取數組。 您還想在其中放置對象而不是數組：

 const res = Object.values(cars.reduce((acc, {group, ...r}) => {
    group.forEach(key => {
      (acc[key] = (acc[key] || { group, cars: [] })).cars.push(r);
    });
    return acc;
 }, {}));

我會這樣寫：

  const byGroup = new Map();

  for(const { group, ...rest } of cars) {
     if(!byGroup.has(group))
       byGroup.set(group, { group, cars: [] });
     byGroup.get(group).cars.push(rest);
  }

  const result = [...byGroup.values()];

Answer 2

您需要將一個對象作為累加器，然后映射條目以獲得所需的結果。

 let cars = [{ group: [], name: "All Makes", code: "" }, { group: ["Group A"], name: "BMW", code: "X821" }, { group: ["Group B"], name: "Audi", code: "B216" }, { group: ["Group B"], name: "Ford", code: "P385" }, { group: ["Group B", "Group C"], name: "Mercedes", code: "H801" }, { group: ["Group C"], name: "Honda", code: "C213" }], result = Object .entries(cars.reduce((acc, { group, ...r }) => { group.forEach(key => acc[key] = (acc[key] || []).concat({...r})); return acc; }, {})) .map(([group, cars]) => ({ group, cars })); console.log(result);

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