使用 reduce 并向结果对象添加另一个值

Question

books 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) 来：返回一个数组，其中包含五个或更少的对象，这些对象代表最常见的流派，从最常见到最少的顺序排列，如下所示：（如果存在超过五本书，则只有顶部五个应该返回。）

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

这是我目前所拥有的：

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

我很确定我已经得到了我需要的一切，除了流派之后的“计数”值。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。

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;
}

Answer 2

这是我创建的用于对您的图书类型进行排序的代码：

function getMostCommonGenres(books) {
    returnStrs = [];
    genres = []; // [["genreName1", 1],["genreName2",1]] The number is the count
    var i;
    for (i = 0; i < books.length; i++) {
        genre = books[i].genre;
        if (!DoesGenreExist(genre, genres)) {
            genres.push([genre, 1]);
        }
    }
    genres.sort(function (a, b) { // Sort genres by the count
        return b[1] - a[1];
    });

    numGenres = genres.length
    if (numGenres > 5) { // take 5 max
        numGenres = 5
    }

    for (i = 0; i < numGenres; i++) {
        var summary = new GenreSummary(genres[i][0], genres[i][1])
        returnStrs.push(JSON.stringify(summary)); // Create genre string and add to return value
    }
    console.log(returnStrs)
    return returnStrs;
}

function DoesGenreExist(genreStr, genres) { // If it exists it also increments the count
    for (i = 0; i < genres.length; i++) {
        if (genres[i][0] == genreStr) {
            genres[i][1]++;
            return true;
        }
    }
    return false;
}

class GenreSummary {
    constructor(name, count) {
        this.name = name;
        this.count = count;
    }
}

我从你的第一个代码 sn-p 输入你的书并得到以下输出：

[ '{"name":"Science","count":1}' ]

Answer 3

您可以使用 reduce 和 slice 轻松实现此目的（获得 5 个元素）

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,
    },
  ],
}, ];

function getMostCommonGenres(books) {
  const result = books.reduce((acc, book) => {
    if (book.borrows.length > 5) {
      acc.push({
        name: book.genre,
        count: book.borrows.length,
      });
    }
    return acc;
  }, []);
  return result.sort((a, b) => b.count - a.count)
               .slice(0, 5);
}

const resultArray = getMostCommonGenres(books);
console.log(resultArray);