javascript - 基于一些计算将复杂的 javascript 数组减少到另一个数组？

Question

我有一个对象数组

data: [
    {
        eventId: "EVEN00001",
        eventType: "call",
        startDate: "2018-08-01T21:30:17+05:30",
    },
    {
        eventId: "EVEN00002",
        eventType: "call",
        startDate: "2018-08-01T21:30:17+05:30",
    },
    {
        eventId: "EVEN00003",
        eventType: "meeting",
        startDate: "2017-02-03T21:30:17+05:30",
    },
    {
        eventId: "EVEN00004",
        eventType: "email",
        startDate: "2018-09-04T21:30:17+05:30",
    },
    {
        eventId: "EVEN00005",
        eventType: "meeting",
        startDate: "2018-09-05T21:30:17+05:30",
    }]

我想把它减少到

[{call: 2},{meeting: 2},{email: 1}]

如何使用 javascript reduce 方法实现此目的，不知何故，我能够达到预期的结果，但这不是正确的方法。

data.reduce((acc, item, i, arr) => {
        if (!acc[item.startDate]) {
            acc[item.startDate] = 1;
        } else {
            acc[item.startDate] += 1;
        }
        return acc;
    }, {});
const dayArray = Object.entries(trimedData)
    .reduce((acc, node, i, arr) => {

        let [days, val] = node;
        acc.push({
            days: days,
            value: val
        })
        return acc;
    }, []);

如何仅使用 reduce. 或任何其他更好的方法来达到预期的结果？

Answer 1

reduce 为由 eventType 索引的对象，其值为该 eventType 到目前为止出现的次数 - 将适当的属性增加每次迭代一个。然后，获取该对象的值:

const data=[{eventId:"EVEN00001",eventType:"call",startDate:"2018-08-01T21:30:17+05:30",},{eventId:"EVEN00002",eventType:"call",startDate:"2018-08-01T21:30:17+05:30",},{eventId:"EVEN00003",eventType:"meeting",startDate:"2017-02-03T21:30:17+05:30",},{eventId:"EVEN00004",eventType:"email",startDate:"2018-09-04T21:30:17+05:30",},{eventId:"EVEN00005",eventType:"meeting",startDate:"2018-09-05T21:30:17+05:30",}]

console.log(Object.values(
  data.reduce((a, { eventType }) => {
    if (!a[eventType]) a[eventType] = { [eventType] : 0 };
    a[eventType][eventType]++;
    return a;
  }, {})
));