将对象数组转换为数组对象答案

【问题标题】：Converting an Array of Objects to an Object of arrays将对象数组转换为数组对象
【发布时间】：2018-12-04 14:17:35
【问题描述】：

假设我有一个对象数组

const data = [{ description: "my frist event", start_time: "11:00", end_time: "12:00", event_day: "22" }, { description: "my second event", start_time: "11:00", end_time: "12:00", event_day: "22" }]

因此，每天都会有一组对象。例如，第 22 天应该在数组中有两个项目。所以结构要采用这种格式

{ 22: [ { description: 'my second event',
   start_time: '11:00',
   end_time: '12:00',
   event_day: '22' }, { description: "my frist event", start_time: "11:00", end_time: "12:00", event_day: "22" } ] }

使用reduce方法

const arrayToObject = (array) =>array.reduce((obj, item) => {
  obj[item.event_day] = [item]
  return obj}, {})
arrayToObject(data)

给我以下输出：

{ 22: [ { description: 'my second event',
   start_time: '11:00',
   end_time: '12:00',
   event_day: '22' } ] }

这只会将最后一项添加到数组中。有没有办法将所有其他对象添加到数组中？

【问题讨论】：

你的回调必须检查obj[item.event_day]是否已经存在。

标签： javascript arrays node.js reactjs javascript-objects

【解决方案1】：

如果累加器对象中不存在event_day对应的数组，则先创建，再将push添加到它：

const data = [{ description: "my frist event", start_time: "11:00", end_time: "12:00", event_day: "22" }, { description: "my second event", start_time: "11:00", end_time: "12:00", event_day: "22" }];
const groupedByDay = data.reduce((a, item) => {
  const { event_day } = item;
  if (!a[event_day]) a[event_day] = [];
  a[event_day].push(item);
  return a;
}, {});
console.log(groupedByDay);

【讨论】：

【解决方案2】：

这也应该有效：

const data = [
  {
    description: 'my frist event',
    start_time: '11:00',
    end_time: '12:00',
    event_day: '22',
  },
  {
    description: 'my second event',
    start_time: '11:00',
    end_time: '12:00',
    event_day: '22',
  },
  {
    description: 'my second event',
    start_time: '11:00',
    end_time: '12:00',
    event_day: '55',
  },
];

const reduced = data.reduce(
  (acc, item) => ({
    ...acc,
    [item.event_day]: data.filter((i) => i.event_day === item.event_day),
  }),
  {}
);

console.log('reduced', reduced);

【讨论】：