如何将数组中的多个对象转换为新对象？

Question

假设我有一个下面的数组：

[
  { type: 'senior', schoolName: 'school-A', country: 'America' },
  { type: 'senior', schoolName: 'school-B', country: 'England' },
  { type: 'junior', schoolName: 'school-C', country: 'German' },
  { type: 'junior', schoolName: 'school-D', country: 'Italy' }, 
]

如何将上面的数组转换为对象，如下所示：

{
  senior: {
    America: 'school-A', 
    England: 'school-B'
  }, 
  junior: {
    German: 'school-C', 
    Italy: 'school-D'
  }
}

完成此任务的语法上最简洁的方法是什么？

谢谢你的帮助！！

Answer 1

一种方法是将对象数组减少为单个对象。对于每次迭代，您可以累积对象（最初作为空对象开始{}），以包含当前type键以及国家/地区和学校名称的新键值对。通过使用扩展语法...，您可以将键处先前看到的对象type（来自当前累积的对象）与您正在构造的新对象合并。

请参阅下面示例中的代码注释：

const arr = [ { type: 'senior', schoolName: 'school-A', country: 'America' }, { type: 'senior', schoolName: 'school-B', country: 'England' }, { type: 'junior', schoolName: 'school-C', country: 'German' }, { type: 'junior', schoolName: 'school-D', country: 'Italy' }, ];

const res = arr.reduce((acc, {type, schoolName, country}) => ({ // obtain the kys from the current object using destructuring assignment
  ...acc, // merge the current object stored in acc into the current object `{}` we're building
  [type]: { // using "computed property names"
    ...acc[type], // merge inner object (still worrks when acc[type] === undefined) 
    [country]: schoolName
  }
}), {}); // start with an initial empty object `{}` that we'll accumulate to
console.log(res);

每次迭代传播对象可能被视为效率低下，因此您可以改为累积单个对象引用（此时，可能值得考虑使用标准循环for来提高可读性）：

const arr = [ { type: 'senior', schoolName: 'school-A', country: 'America' }, { type: 'senior', schoolName: 'school-B', country: 'England' }, { type: 'junior', schoolName: 'school-C', country: 'German' }, { type: 'junior', schoolName: 'school-D', country: 'Italy' }, ];

const res = arr.reduce((acc, {type, schoolName, country}) => {
  if(!acc[type]) acc[type] = {};
  acc[type][country] = schoolName;
  return acc;
}, {});
console.log(res);