Lodash - 如何计算数组中的出现次数

Question

假设我们有一个数组：

const pets = ['Dog','Cat','Fish','Dog','Dog','Cat']

如何使用 lodash 以这种格式返回最常出现的对象？

{
  pet: 'Dog',
  number: 3
}

Answer 1

const pets = ['Dog', 'Cat', 'Fish', 'Dog', 'Dog', 'Cat'];
const frequency =  _.maxBy(_.map(_.groupBy(pets), pet => ({ pet: pet[0], number: pet.length })), 'number');
console.log(frequency);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>

Answer 2

您可以使用_.countBy() 计算数组中宠物的频率。然后您可以获取频率条目并使用_.maxBy() 找到最大条目。获得最大条目后，您可以将其映射到对象：

const popularPet = _.flow(
  _.countBy,
  o => _.maxBy(_.entries(o), _.last),
  ([pet, number]) => ({pet, number})
);

const res = popularPet(['Dog','Cat','Fish','Dog','Dog','Cat']);
console.log(res);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>

Answer 3

const pets = ['Dog','Cat','Fish','Dog','Dog','Cat'];
const petsGrpByDups = _.groupBy(pets);
console.log('******* GROUPBY DUPS *******');
console.log(petsGrpByDups);

let mostFreqOccs = _.reduce(petsGrpByDups, ({number,pet}, elem) => {
  return elem.length > number 
         ? {number:elem.length, pet: elem[0]} 
         : {number, pet };
}, {number:0});

console.log('******* MOST FREQ OCCURRED *******');
console.log(mostFreqOccs);

mostFreqOccs = _.maxBy(_.values(petsGrpByDups), elem => elem.length);

console.log('******* MOST FREQ OCCURRED *******');
console.log(mostFreqOccs);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.js"></script>

Answer 4

如果你对 lodash 不是很挑剔，下面是带有 forEach 和 Object.entries 的纯 JS

const pets = ["Dog", "Cat", "Fish", "Dog", "Dog", "Cat"];

const words = {};
pets.forEach((word) => (words[word] = (words[word] ?? 0) + 1));

const [[pet, number]] = Object.entries(words).sort(([, a], [, b]) => b - a);

const result = { pet, number };

console.log(result);