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javascript - 使用 JavaScript .map() 和 .filter() 按语言搜索作者/书籍数据模块

问题描述

我想books.lang使用.map()和按语言搜索以下数据模块.filter()。如果没有定义语言，则该函数返回所有具有相关书籍的作者。如果请求一种语言，则该函数仅返回将书籍翻译成该语言的作者。

数据模块如下：

// data.js
const authors = [
  {
    id: 1,
    name: "Author 1"
  },
  {
    id: 2,
    name: "Author 2"
  },
  {
    id: 3,
    name: "Author 3"
  }
];

const books = [
  {
    id: 1,
    authorId: 1,
    lang: "IT",
    title: "Title 1",
    date: "2018-06-07"
  },
  {
    id: 2,
    authorId: 1,
    lang: "EN",
    title: "Title 2",
    date: "2018-06-07"
  },
  {
    id: 3,
    authorId: 2,
    lang: "IT",
    title: "Title 1",
    date: "2018-06-07"
  },
  {
    id: 4,
    authorId: 2,
    lang: "FR",
    title: "Title 2",
    date: "2018-06-07"
  },
  {
    id: 5,
    authorId: 3,
    lang: "IT",
    title: "Title 1",
    date: "2018-07-07"
  }
];

module.exports = { authors, books };

一个常见的解决方案是使用经典的 for 循环。但我无法找到正确的解决方案，仅使用.map()并.filter()最终链接它们，它不会按作者对书籍进行分组。对于每个作者，我创建一个books属性来对相关书籍进行分组。

经典的工作解决方案如下：

const lang = "IT";

filtered_books = books.filter( book => lang !== null ? book.lang == lang : book.lang !== '' ); 

for (let i in authors) {
    authors[i].books = filtered_books.filter( book => book.authorId == authors.id);
}

这是我坚持我的.map()解决方案的地方.filter()：

const lang = "IT";

const selectedAuthors = books.filter( book => lang !== null ? book.lang == lang : book.lang !== '' )
                             .map( book => { 
                                 return authors.filter( author => { 
                                     if(author.id == book.authorId) return author.books = book; // Should I push something here?
                             });
                         });

不管有没有这个lang参数，它都不会按作者对结果书进行分组。

非常感谢您的任何建议。

标签： javascriptfunctional-programming

解决方案

我看起来像一个两阶段的通行证 - 1）将作者与他们的书籍结合起来，2）过滤掉那些拥有指定语言书籍的作者。

const authors = [{"id":1,"name":"Author 1"},{"id":2,"name":"Author 2"},{"id":3,"name":"Author 3"}];
const books = [{"id":1,"authorId":1,"lang":"IT","title":"Title 1","date":"2018-06-07"},{"id":2,"authorId":1,"lang":"EN","title":"Title 2","date":"2018-06-07"},{"id":3,"authorId":2,"lang":"IT","title":"Title 1","date":"2018-06-07"},{"id":4,"authorId":2,"lang":"FR","title":"Title 2","date":"2018-06-07"},{"id":5,"authorId":3,"lang":"IT","title":"Title 1","date":"2018-07-07"}];

function findBooks(authors, books, lng) {

  // map over the books and get their books
  const combined = authors.map(author => {
    const filteredBooks = lng
      ? books.filter(book => book.authorId === author.id && book.lang === lng)
      : books.filter(book => book.authorId === author.id)
    return { ...author, books: filteredBooks };
  });

  // if a language has been specified, return only those authors who have books
  // in that language
  return lng ? combined.filter(author => author.books.some(book => book.lang === lng)) : combined;
}

const authorBooks = findBooks(authors, books);
console.log(authorBooks);

const authorBooksLng = findBooks(authors, books, 'EN');
console.log(authorBooksLng);

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