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"},
]

现在如何在对象 teaherList

中找到每个 [teacherID:,teacherName:] 的频率]

目前我在做什么，

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出现的频率，但是有没有更好、更高效的方法来完成这项任务

Answer 1

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

let count1 = countBy(temp);
console.log(count1) // object
//(1:3,2:3,3:3)

如果有更好的解决方法，请告诉我

Answer 2

假设teaherList是一个对象数组，这里有一个不需要依赖于库的方法，并且还一次性创建了输出对象（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 })
  ), {})
);

Answer 3

我修改了这个 teaherList 一点，因为那不是有效的对象。你可以尝试这样的事情，结果数组将是这样的 [{teacherID1: teacherName1}, {teacherID2: teacherName2}].

var 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"},
]
var result = teaherList.reduce(function(acc, cV) {
if(!acc[cV.teacherName]) {
acc[cV.teacherName]= {teacherID: cV.teacherID,
teacherName: cV.teacherName, 
count: 1};
} else {
acc[cV.teacherName].count++;
}
return acc;
}, {});

console.log(result);

希望对您有所帮助。

Answer 4

您可以使用 Array#forEach 为每个循环分配对象和返回对象而不会产生开销。

var teacherList = [{ 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" }],
    frequency = Object.create(null);
    
teacherList.forEach(({ teacherName }) => frequency[teacherName] = (frequency[teacherName] || 0) + 1);

console.log(frequency);

Answer 5

这是使用 while 循环的另一种方法。

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"}];

const calculateFrequencies = ({ input, output = Object.create(null), id, name, 
                                start: i = 0, end = input.length }) => {
    while(i < end && ({ teacherID: id, teacherName: name } = input[i++]))
        ++(output[id] || (output[id] = { id, name, count: 0 })).count;
    
    return Object.values(output);
}

console.log(calculateFrequencies({ input: teaherList }));

在 javascript 中查找对象中键值对的频率

finding the frequency of a key value pair in an object in javascript

javascript

arrays

object

frequency

find-occurrences