javascript - 在javascript中查找对象中键值对的频率

Question

假设我有一个对象

teaherList = [
{teacherID:1,teacherName:"john"},
{teacherID:2,teacherName:"joe"},
{teacherID:3,teacherName:"jill"},
{teacherID:1,teacherName:"john"},
{teacherID:2,teacherName:"joe"},
{teacherID:3,teacherName:"jill"},
{teacherID:1,teacherName:"john"},
{teacherID:2,teacherName:"joe"},
{teacherID:3,teacherName:"jill"},
]

现在我如何在对象teaherList 中找到每个 [teacherID:,teacherName:] 的频率

目前我的情况是，

let temp = []
_.each(teaherList, function(k){
   temp.push(k.teacherID)
)

let count1 = countBy(temp);

它给出了对象中教师出现的频率，但是有没有更好和更有效的方法来完成这项任务

Answer 1

假设 teaherList 是一个对象数组，这是一个不需要依赖库的方法，并且还可以一次性创建输出对象(总迭代次数 = 数组长度), reduce:

const teaherList = [
  {teacherID:1,teacherName:"john"},
  {teacherID:2,teacherName:"joe"},
  {teacherID:3,teacherName:"jill"},
  {teacherID:1,teacherName:"john"},
  {teacherID:2,teacherName:"joe"},
  {teacherID:3,teacherName:"jill"},
  {teacherID:1,teacherName:"john"},
  {teacherID:2,teacherName:"joe"},
  {teacherID:3,teacherName:"jill"},
];
console.log(
  teaherList.reduce((a, { teacherName }) => (
    Object.assign(a, { [teacherName]: (a[teacherName] || 0) + 1 })
  ), {})
);