javascript - 对特定属性具有相同值的元素进行计数，并将结果放入对象数组中

Question

使用 Array.reduce ，我正在尝试计算对特定属性具有相同值的元素。我想将结果放入一个对象数组中，其中包含一个用于按属性分组的值的属性和另一个用于计数的属性。我怎样才能在 javascript 中轻松做到这一点？

const CATEGORY = {
  STRATEGY: 'STRATEGY',
  CONTENT: 'CONTENT',
  ADVERTISING: 'ADVERTISING',
  MEASURMENT: 'MEASURMENT'
}

const lessons = [
  {
    title: 'ohoho',
    category: CATEGORY.STRATEGY
  }, {
    title: 'hihihi',
    category: CATEGORY.CONTENT
  }, {
    title: 'hello',
    category: CATEGORY.CONTENT
  }
]

let categoryLessonCount = lessons.reduce(function (acc, lesson) {
  acc[lesson.category] ? acc[lesson.category]++ : acc[lesson.category] = 1
  return acc
}, {})
console.log(categoryLessonCount[CATEGORY.STRATEGY])
console.log(categoryLessonCount[CATEGORY.CONTENT])

实际 categoryLessonCount 值:

Object
{
  STRATEGY: 1, 
  CONTENT: 2
}

想要的 categoryLessonCount 值:

Array
[ 
  {
   title: 'STRATEGY', 
   count: 1
  }, {
   title: 'CONTENT', 
   count: 2
  } 
]

Answer 1

你已经得到了你想要的只是将它转换成一个数组

const CATEGORY = {
  STRATEGY: 'STRATEGY',
  CONTENT: 'CONTENT',
  ADVERTISING: 'ADVERTISING',
  MEASURMENT: 'MEASURMENT'
}

const lessons = [{
  title: 'ohoho',
  category: CATEGORY.STRATEGY
}, {
  title: 'hihihi',
  category: CATEGORY.CONTENT
}, {
  title: 'hello',
  category: CATEGORY.CONTENT
}]

let count = lessons.reduce(function(acc, lesson) {
  acc[lesson.category] ? acc[lesson.category] ++ : acc[lesson.category] = 1
  return acc
}, {})

// transform count into what you want
let categoryLessonCount = [];
for (let cat in count) {
  categoryLessonCount.push({
    'title': cat,
    'count': count[cat]
  });
}

console.log(categoryLessonCount)