如何将数组中的多个对象转换为新对象？

Question

假设我在下面有一个数组：

[
  { 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如下所示的对象：

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

在语法上最简洁的方法是什么？

感谢您的帮助！！

Answer 1

一种方法是将reduce 您的对象数组转换为单个对象。对于每次迭代，您可以累积您的对象（最初从一个空对象 {} 开始），以包含当前的 type 键以及国家和学校名称的新键值对。通过使用spread syntax ...，您可以将先前在type 键处看到的对象（来自您当前累积的对象）与您正在构建的新对象合并。

请参阅下面示例中的代码 cmets：

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，因此您可以累积单个对象引用（此时，为了提高可读性，可能值得考虑使用标准 for 循环）：

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);

Answer 2

我认为这是解决您的问题的简单易读的解决方案（如果同一 country 的多个实例出现在同一 type 中，则最后一次出现将覆盖所有以前的出现）

let data = [
  { 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' }, 
];

let res = {};

data.forEach(e => {
  if(!res[e.type])
    res[e.type] = {};
    
  res[e.type][e.country] = e.schoolName;
});

console.log(res);