需要帮助返回一个包含两个数组的数组：借书和还书

Question

我试图返回一个包含两个数组的数组，第一个是借来的书，另一个是归还的书。我必须使用的提示是：

public/src/books.js 中的partitionBooksByBorrowedStatus() 函数只有一个参数：

• 一系列书籍。

它返回一个包含两个数组的数组。所有输入的书籍都存在于第一个或第二个数组中。

第一个数组包含已借出但尚未归还的图书，而第二个数组包含已归还的图书。您可以检查是否归还通过查看borrows 数组中的第一笔交易来查看状态。

以下是提供的部分数据：

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,
  },

这是我迄今为止尝试过的：

function partitionBooksByBorrowedStatus(books) {

  let available = [];
  let unavailable = [];
  const bookStatuses = [];

  books.forEach((book) => {
   const isBookReturned = book.borrows[0].returned;
   if (isBookReturned) { // if book is returned
     available.push(book);
   } else { // if book is not returned
     unavailable.push(book);
   }
 });

 bookStatuses.push(available);
 bookStatuses.push(unavailable);

 return bookStatuses; //

}

当我运行代码时，它会返回一个错误，指出“预期 3 等于 6”，我这辈子都想不通。非常感谢您的 cmets 和建议，谢谢！

Answer 1

感谢@Dave Newton，他提到我返回的数组似乎是向后的，我能够交换返回值，所以现在正确的代码是：

function partitionBooksByBorrowedStatus(books) {
let available = [];
let unavailable = [];
const bookStatuses = [];
books.forEach((book) => {
  const isBookReturned = book.borrows[0].returned;

if (isBookReturned) { // if book is not returned
  unavailable.push(book);
} else { // if book is returned
  available.push(book);
}
});
bookStatuses.push(available);
bookStatuses.push(unavailable);
return bookStatuses;
}

Answer 2

这可以通过 JavaScript 的 Array reduce 方法轻松完成。您需要为初始累加器提供一个映射预期输出的对象，然后根据图书是否至少出现一次未返回的图书来填充两个数组之一。 （也可以通过测试“returned == false”的个数是否为奇数）。

假设 1：一本从未被借过的书应该算作“被归还” 假设 2：“书”是 ISBN 的字面上唯一的个人副本。

更正：没有看到借用数组的第一个元素指示当前状态。

const books = [
{
    id: "0",
    title: "never borrowed",
    genre: "Science",
    authorId: 8,
    borrows: []
},
{
    id: "1",
    title: "returned",
    genre: "Science",
    authorId: 8,
    borrows: [
        {
            id: "5f446f2e2f35653fa80bf490",
            returned: true,
        }
    ]
},
{
    id: "5f447132d487bd81da01e25e",
    title: "not returned",
    genre: "Science",
    authorId: 8,
    borrows: [
        {
            id: "5f446f2e2cfa3e1d234679b9",
            returned: false,
        }
    ]
}]

function partitionBooksByBorrowedStatus(b) {
    return b.reduce( (a, c) => { a[+(c.borrows[0] && c.borrows[0].returned)].push(c); return a }, [[],[]] )
}

console.log(partitionBooksByBorrowedStatus(books))