如何映射对象数组并将其返回为在"类别"中排序的对象的新数组[重复]

Question

我正在构建我的第一个react原生应用程序，我想向用户展示一些按类别划分的“追随者”屏幕，但要做到这一点，我想我必须从我拥有的东西中创建新的对象数组。

我有这样的对象数组：

followers: [
    {
      userId: 2,
      userName: "Abigail",
      followDate: "1980-04-09T10:15:30+07:00",
      category: "A"
    },
    {
      userId: 3,
      userName: "John",
      followDate: "1980-04-09T10:15:30+07:00",
      category: "B"
    },
    {
      userId: 4,
      userName: "Bob",
      followDate: "1980-04-09T10:15:30+07:00",
      category: "A"
    },
    {
      userId: 5,
      userName: "Martha",
      followDate: "1980-04-09T10:15:30+07:00",
      category: "B"
    } 
]

现在我想把这些追随者呈现给用户，这些追随者由追随者数组对象中的类别分开。因此，我认为我需要创建新的对象数组，我认为它应该如下所示：

followersSortedByCategory = [
      {
        category: "A",
        followers: [
          {
            userId: 2,
            userName: "Abigail",
            followDate: "1980-04-09T10:15:30+07:00",
            category: "A"
          },
          {
            userId: 4,
            userName: "Bob",
            followDate: "1980-04-09T10:15:30+07:00",
            category: "A"
          }
        ]
      },
      {
        category: "B",
        followers: [
          {
            userId: 3,
            userName: "John",
            followDate: "1980-04-09T10:15:30+07:00",
            category: "B"
          },
          {
            userId: 5,
            userName: "Martha",
            followDate: "1980-04-09T10:15:30+07:00",
            category: "B"
          }
        ]
      }
    ]

没有很多“如果”，我不确定如何做到这一点。我认为有一个很好的方法，使用地图，过滤器等功能，但我不知道如何做。

Answer 1

所有这些答案可能会使用减少，它们可能都一样好。但是他们都使用了微妙不同的数据迭代方法。这种方法使用对象键

let categories = Object.values(
// the final output will be an array
    data.followers.reduce( (b,a) => {
    // we iterate the followers and build the accumulator object
    if (b.hasOwnProperty(a.category)) b[a.category].followers.push(a)
    // if our accumulating object already has the category key, add to the follower array
    else b[a.category] = {category: a.category, followers: [a]}
    // otherwise create the object key and initialize it with the first follower
    return b
    },{}))

let data = {
  followers :[
  { userId: 2, userName: "Abigail", followDate: "1980-04-09T10:15:30+07:00", category: "A" },
  { userId: 3, userName: "John", followDate: "1980-04-09T10:15:30+07:00", category: "B" },
  { userId: 4, userName: "Bob", followDate: "1980-04-09T10:15:30+07:00", category: "A" },
  { userId: 5, userName: "Martha", followDate: "1980-04-09T10:15:30+07:00", category: "B" } 
]}

let categories = Object.values(data.followers.reduce( (b,a) => {
if (b.hasOwnProperty(a.category)) b[a.category].followers.push(a)
else b[a.category] = {category: a.category, followers: [a]}
return b
},{}))

console.log(categories)

Answer 2

const followers = [
  { userId: 2, userName: "Abigail", followDate: "1980-04-09T10:15:30+07:00", category: "A" },
  { userId: 3, userName: "John", followDate: "1980-04-09T10:15:30+07:00", category: "B" },
  { userId: 4, userName: "Bob", followDate: "1980-04-09T10:15:30+07:00", category: "A" },
  { userId: 5, userName: "Martha", followDate: "1980-04-09T10:15:30+07:00", category: "B" } 
];

const followersSortedByCategory = [...
  // iterate over followers array while updating categoryMap (category-records)
  followers.reduce((categoryMap, follower) => {
    const { category } = follower;
    // get record of follower's category if exists
    const categoryRecord = categoryMap.get(category);
    if(!categoryRecord) { // if not, add new pair
      categoryMap.set(category, { category, followers: [follower] });
    } else { // else update the record's followers array
      categoryRecord.followers.push(follower);
    }
    return categoryMap;
  }, new Map)
  // return grouped list by categories
  .values()
];

console.log(followersSortedByCategory);

Answer 3

较短的解决方案：

const followers = [
{
  userId: 2,
  userName: "Abigail",
  followDate: "1980-04-09T10:15:30+07:00",
  category: "A"
},
{
  userId: 3,
  userName: "John",
  followDate: "1980-04-09T10:15:30+07:00",
  category: "B"
},
{
  userId: 4,
  userName: "Bob",
  followDate: "1980-04-09T10:15:30+07:00",
  category: "A"
},
{
  userId: 5,
  userName: "Martha",
  followDate: "1980-04-09T10:15:30+07:00",
  category: "B"
} 
]

function formatFollowers(followers){
  const categories = [...new Set(followers.map(follower=> follower.category))]
   return categories.reduce((acc, category)=> {
     const _followers = followers.filter(follower=> follower.category === category)
    return [...acc, {category: category, followers: _followers}]
  }, [])
}

console.log(formatFollowers(followers))