如何在JavaScript中按日期聚合对象数组的主题与计数？

我有一个包含created_at、topic和count字段的对象数组，需要将其转换为按日期分组的结构：每个日期对应一个对象，以各类topic作为键，对应的count数值作为值。我尝试用reduce方法实现，以下是原始数组和期望转换结果：

原始数组 #

const myObj = [
{
    "created_at": "2022-06-12T18:30:00.000Z",
    "topic": "Technical_support/Installation",
    "count": "2"
},
{
    "created_at": "2022-06-10T18:30:00.000Z",
    "topic": "pricing",
    "count": "1"
},
{
    "created_at": "2022-06-10T18:30:00.000Z",
    "topic": "Product/sales enquiry",
    "count": "1"
},
{
    "created_at": "2022-06-10T18:30:00.000Z",
    "topic": "Service",
    "count": "4"
},
{
    "created_at": "2022-06-10T18:30:00.000Z",
    "topic": "others",
    "count": "1"
},
{
    "created_at": "2022-06-12T18:30:00.000Z",
    "topic": "Product/sales enquiry",
    "count": "5"
},
{
    "created_at": "2022-06-11T18:30:00.000Z",
    "topic": "Service",
    "count": "28"
},
{
    "created_at": "2022-06-11T18:30:00.000Z",
    "topic": "Billing/order",
    "count": "1"
},
{
    "created_at": "2022-06-12T18:30:00.000Z",
    "topic": "Service",
    "count": "11"
},
{
    "created_at": "2022-06-12T18:30:00.000Z",
    "topic": "others",
    "count": "5"
},
{
    "created_at": "2022-06-10T18:30:00.000Z",
    "topic": "Technical_support/Installation",
    "count": "1"
},
{
    "created_at": "2022-06-11T18:30:00.000Z",
    "topic": "pricing",
    "count": "6"
},
{
    "created_at": "2022-06-12T18:30:00.000Z",
    "topic": "pricing",
    "count": "1"
},
{
    "created_at": "2022-06-10T18:30:00.000Z",
    "topic": "offer",
    "count": "1"
},
{
    "created_at": "2022-06-11T18:30:00.000Z",
    "topic": "Product/sales enquiry",
    "count": "4"
},
{
    "created_at": "2022-06-11T18:30:00.000Z",
    "topic": "offer",
    "count": "1"
},
{
    "created_at": "2022-06-11T18:30:00.000Z",
    "topic": "others",
    "count": "15"
},
{
    "created_at": "2022-06-11T18:30:00.000Z",
    "topic": "Technical_support/Installation",
    "count": "10"
}
]

期望转换结果 #

（注：你提供的示例结果中部分数值与原始数组不符，以下是基于原始数组计算出的正确结果）

[
  {
    date: "2022-06-10T18:30:00.000Z",
    "Technical_support/Installation": 1,
    pricing: 1,
    "Product/sales enquiry": 1,
    Service: 4,
    others: 1,
    offer: 1
  },
  {
    date: "2022-06-11T18:30:00.000Z",
    Service: 28,
    "Billing/order": 1,
    pricing: 6,
    "Product/sales enquiry": 4,
    offer: 1,
    others: 15,
    "Technical_support/Installation": 10
  },
  {
    date: "2022-06-12T18:30:00.000Z",
    "Technical_support/Installation": 2,
    "Product/sales enquiry": 5,
    Service: 11,
    others: 5,
    pricing: 1
  }
];

实现方案 #

基础分组实现 #

使用Array.reduce()完成分组，同时将字符串类型的count转为数字：

const groupedByDate = Object.values(myObj.reduce((acc, item) => {
  const date = item.created_at;
  // 初始化当前日期的对象
  if (!acc[date]) {
    acc[date] = { date };
  }
  // 赋值或累加count数值
  acc[date][item.topic] = (acc[date][item.topic] || 0) + Number(item.count);
  return acc;
}, {}));

包含所有Topic的实现 #

如果需要每个日期对象都包含所有出现过的topic（无数据时显示0），可以先收集所有唯一topic再初始化：

// 提取所有唯一的topic
const allTopics = [...new Set(myObj.map(item => item.topic))];

const groupedByDateWithAllTopics = Object.values(myObj.reduce((acc, item) => {
  const date = item.created_at;
  if (!acc[date]) {
    // 初始化时给所有topic设置默认值0
    acc[date] = allTopics.reduce((topicAcc, topic) => {
      topicAcc[topic] = 0;
      return topicAcc;
    }, { date });
  }
  // 累加对应topic的count
  acc[date][item.topic] += Number(item.count);
  return acc;
}, {}));

代码说明 #

1. reduce累加器：用空对象存储日期到对应数据对象的映射。
2. 日期分组：遍历每个元素，以created_at为键，不存在则创建包含date字段的对象。
3. 数值处理：将count转为数字，若当前topic已存在则累加，否则从0开始累加。
4. 转换为数组：通过Object.values()将累加器中的对象提取为最终的数组结构。

内容的提问来源于stack exchange，提问作者Priyansh Sharma