JavaScript Object Literal - 数据操作答案

【问题标题】：JavaScript Object Literal - Data ManipulationJavaScript Object Literal - 数据操作
【发布时间】：2019-11-26 08:54:51
【问题描述】：

我有一个对象字面量，其中包含一组对象（它们是书籍）和方法，我需要获取具有最多“书籍”的“发布者”属性，但我不知道该怎么做。

这是我到目前为止所做的：

const Library = {
  _books: [
    {
      title: 'World of Warcraft: Cycle of Hatred',
      author: 'Keith DeCandido',
      publisher: 'Pocket Star',
      year: 2006
    }
  ],
  // Add Books Method
  addBook: function(book) {
    return typeof book === 'object' ? this._books.push(book) : console.log(`Please enter a valid book.`);
  },
  // Publisher w/ Most Books
  manyBooks: function() {
    return this._books.reduce((books, book) => book.publisher)
  }
}

// Add Books to the Library
Library.addBook({
  title: 'The Witcher: The Last Wish',
  author: 'Andrzej Sapkowski',
  publisher: 'Ciela',
  year: 2016
});

Library.addBook({
  title: 'Fire and Blood',
  author: 'George Martin',
  publisher: 'Bard',
  year: 2019
});

Library.addBook({
  title: 'Song of Fire and Ice',
  author: 'George Martin',
  publisher: 'Bard',
  year: 2001
});

// Print results in the console
console.log(`Total Books in the Library:`, Library.getBooks());
console.log(`Publisher With Most Books:`,  Library.manyBooks());

这是我的完整代码：https://repl.it/@natefr0st/Objects

【问题讨论】：

请同时添加 wanred 结果。如果所有出版商的图书数量相同会怎样？

标签： javascript arrays json object ecmascript-6

【解决方案1】：

您可以按出版商对图书进行分组，然后获取图书数量最多的出版商。

const groupBy = (items, key) => items.reduce(
  (result, item) => ({
    ...result,
    [item[key]]: [
      ...(result[item[key]] || []),
      item,
    ],
  }), 
  {},
);

...

// Publisher w/ Most Books
manyBooks: function() {
    publishers = groupBy(this._books, "publisher")

    return Object.keys(publishers)
                 .reduce((a, b) => publishers[a] > publishers[b] ? a : b)
}

groupBy 可以看起来像只返回计数而不是书籍列表：

const groupBy = (items, key) => items.reduce(
  (result, item) => ({
    ...result,
    [item[key]]: (result[item[key]] || 0) + 1,
  }), 
  {},
);

manyBooks 函数获取最大书籍的出版商列表：

manyBooks: function() {
    publishers = groupBy(this._books, "publisher")
    maxCount = Math.max(...Object.values(publishers))
    return Object.keys(publishers) 
                 .filter((val) => publishers[val] == maxCount);
  }
}

【讨论】：

【解决方案2】：

我会首先将一个对象与每个出版商的书籍聚合起来：

var publishers = this._books.reduce((publishers, book) => { 
   publishers[book.publisher] = (publishers[book.publisher]||0)+1;
   return publishers;
}, {});

然后您可以对该对象的键进行排序：

var publishersByBooks = Object.keys(publishers).sort((a,b) => publishers[a] == publishers[b] ? 0 : publishers[a] > publishers[b] ? -1 : 1);

这样，publishersByBooks[0] 将成为拥有最多书籍的出版商。 publishersByBooks[1] 可能有也可能没有同样多的书。你想用它做什么取决于你的实现。您可以访问publishers[publishersByBooks[0]] 以获取该出版商的图书数量。

【讨论】：

当我尝试 console.log 它console.log(`Publisher With Most Books:`, Library.manyBooks()); 它返回“出版商最多的书：未定义” 我使用的方法：manyBooks: function() { // return this._books.reduce((books, book) => book.publisher) this._books.reduce((publishers, book) => { publishers[book.publisher] = (publishers[book.publisher] || 0) + 1; return publishers; }, {}); }
@KevinZino：您注释掉的行有一个返回语句，现在丢失了。现在，manyBooks 没有返回任何内容。

【解决方案3】：

const Library = {
  _books: [
    {
      title: 'World of Warcraft: Cycle of Hatred',
      author: 'Keith DeCandido',
      publisher: 'Pocket Star',
      year: 2006
    }
  ],
  // Add Books Method
  addBook: function(book) {
    return typeof book === 'object' ? this._books.push(book) : console.log(`Please enter a valid book.`);
  },
  // Publisher w/ Most Books
  manyBooks: function() {
    return this._books.reduce((books, book) => book.publisher)
  },
  
  getBooks(){
   listOfBooks= this._books.map(element => {
      return element
    });
    return listOfBooks
    
    },    
    manyBooks(){
   listOfBooks= this._books.map(element => {
      return element.publisher
    });
    return listOfBooks
    
    }
}

// Add Books to the Library
Library.addBook({
  title: 'The Witcher: The Last Wish',
  author: 'Andrzej Sapkowski',
  publisher: 'Ciela',
  year: 2016
});

Library.addBook({
  title: 'Fire and Blood',
  author: 'George Martin',
  publisher: 'Bard',
  year: 2019
});

Library.addBook({
  title: 'Song of Fire and Ice',
  author: 'George Martin',
  publisher: 'Bard',
  year: 2001
});

console.log(`Total Books in the Library:`, Library.getBooks());
console.log(`Publisher With Most Books:`,  Library.manyBooks());

【讨论】：