在javascript中查找对象中键值对的频率

Question

想象我有一个对象

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"},
]

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

目前我在做的是,

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

let count1 = countBy(temp);

好吧,它给出了对象中教师发生的频率,但有一种更好,更高效的方法来完成这项任务

Answer 1

假设teaherList是一个对象数组,这里的方法不需要依赖于库,并且一次创建输出对象(总迭代次数=数组长度),其中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 })
  ), {})
);