javascript - 使用 reduce 并向结果对象添加另一个值

Question

书籍数组中的对象示例：

const books = [
  {
    id: "5f447132d487bd81da01e25e",
    title: "sit eiusmod occaecat eu magna",
    genre: "Science",
    authorId: 8,
    borrows: [
      {
        id: "5f446f2e2cfa3e1d234679b9",
        returned: false,
      },
      {
        id: "5f446f2ed3609b719568a415",
        returned: true,
      },
      {
        id: "5f446f2e1c71888e2233621e",
        returned: true,
      },
      {
        id: "5f446f2e6059326d9feb9a68",
        returned: true,
      },
      {
        id: "5f446f2ede05a0b1e3394d8b",
        returned: true,
      },
      {
        id: "5f446f2e4081699cdc6a2735",
        returned: true,
      },
      {
        id: "5f446f2e3900dfec59489477",
        returned: true,
      },
      {
        id: "5f446f2e6059326d9feb9a68",
        returned: true,
      },
      {
        id: "5f446f2e409f8883af2955dd",
        returned: true,
      },
      {
        id: "5f446f2e3900dfec59489477",
        returned: true,
      },
      {
        id: "5f446f2eae901a82e0259947",
        returned: true,
      },
      {
        id: "5f446f2ef2ab5f5a9f60c4f2",
        returned: true,
      },
      {
        id: "5f446f2ea6b68cf6f85f6e28",
        returned: true,
      },
      {
        id: "5f446f2eed18105706d6ca19",
        returned: true,
      },
      {
        id: "5f446f2eae901a82e0259947",
        returned: true,
      },
      {
        id: "5f446f2e91c2af00cb74e82b",
        returned: true,
      },
      {
        id: "5f446f2e5aa2bb5545a0f8a6",
        returned: true,
      },
      {
        id: "5f446f2ea508b6a99c3e42c6",
        returned: true,
      },
      {
        id: "5f446f2e50cc2da9cd80efdb",
        returned: true,
      },
      {
        id: "5f446f2e0b3e2ff72fc503e7",
        returned: true,
      },
      {
        id: "5f446f2e91c2af00cb74e82b",
        returned: true,
      },
      {
        id: "5f446f2ef795e593cd3cd19d",
        returned: true,
      },
      {
        id: "5f446f2e2f35653fa80bf490",
        returned: true,
      },
      {
        id: "5f446f2e7b9cd304fed3a8bc",
        returned: true,
      },
      {
        id: "5f446f2ed9aac23c0340aab2",
        returned: true,
      },
    ],
  },

我需要我的函数getMostCommonGenres(books)：返回一个包含五个或更少对象的数组，这些对象代表最常见的流派，从最常见到最少排序，如下所示：（如果存在超过五本书，则只应返回前五名。）

getMostCommonGenres(books);
  [
    { name: "Nonfiction", count: 9 },
    { name: "Historical Fiction", count: 7 },
    { name: "Thriller", count: 7 },
    ...
  ]

这是我到目前为止所拥有的：

function getMostCommonGenres(books) {
  const genreArray = books.reduce((acc, book) => {
    acc[book.name] = book.genre;
    return acc;
  }, {});
}

我很确定除了流派之后的“计数”值之外，我已经得到了我需要的一切。我不确定如何将它添加到对象中。我也不确定如何阻止前五名的计数。我刚刚完成了课程中的高级功能部分，所以我应该使用 forEach、find、filter、some、every、reduce 或 sort。我也不允许使用单字母变量。提前感谢您的任何帮助。

标签： javascriptarraysfunctionjavascript-objects

Answer 1

我得到的答案似乎没有用，但这对我有用：

function getMostCommonGenres(books) {
  const bookGenres = books.map((book) => book.genre);
  const temp = [];
  //map over book genres
  bookGenres.map((genre) => {
    //for each genre, first check to see if genre already exists in array
    const genreLocation = temp.findIndex((element) => element.name === genre);
    //second, if it exists, increase count by 1
    if (genreLocation >= 0) {
      temp[genreLocation].count = temp[genreLocation].count + 1;
      //else, if it don't exist, push a new genre object onto array with count of 1
    } else {
      temp.push({ name: genre, count: 1 });
    }
  });
  temp.sort((a, b) => b.count - a.count);
  if (temp.length > 5) {
    return temp.slice(0, 5);
  }
  return temp;
}