JavaScript 为数组中不存在的键添加零

Question

我有两个数组:

date_array = ["2020-02-27", "2020-02-28", "2020-02-29", "2020-03-01", "2020-03-02", "2020-03-03", "2020-03-04", "2020-03-05", "2020-03-06", "2020-03-07", "2020-03-08", "2020-03-09", "2020-03-10", "2020-03-11", "2020-03-12", "2020-03-13", "2020-03-14", "2020-03-15", "2020-03-16", "2020-03-17", "2020-03-18", "2020-03-19", "2020-03-20", "2020-03-21", "2020-03-22", "2020-03-23", "2020-03-24", "2020-03-25", "2020-03-26", "2020-03-27"]

和

count_array=[{date: "2020-03-22", count: 310},
 {date: "2020-03-23", count: 115},
 {date: "2020-03-24", count: 78},
 {date: "2020-03-25", count: 29},
 {date: "2020-03-26", count: 36},
 {date: "2020-03-27", count: 3}]

我需要创建第三个数组，其中包含 30 个仅具有计数值的元素，如果当天不存在计数，则返回 0。我如何实现这一点？

我试过:

date_array.forEach(element => {
                if (
                  data[date_array.indexOf(element)].date ==
                  date_array[element]
                ) {
                  target_array.push(data[data.indexOf(element)].count_array);
                } else {
                  target_array.push(0);
                }
            });

但我收到“无法读取未定义的属性‘日期’”

Answer 1

为了降低计算复杂度，首先将数组转换为以日期为索引的对象。然后，要制作输出数组，只需 .map date_array 通过查找对象上的日期，与 0 交替:

date_array = ["2020-02-27", "2020-02-28", "2020-02-29", "2020-03-01", "2020-03-02", "2020-03-03", "2020-03-04", "2020-03-05", "2020-03-06", "2020-03-07", "2020-03-08", "2020-03-09", "2020-03-10", "2020-03-11", "2020-03-12", "2020-03-13", "2020-03-14", "2020-03-15", "2020-03-16", "2020-03-17", "2020-03-18", "2020-03-19", "2020-03-20", "2020-03-21", "2020-03-22", "2020-03-23", "2020-03-24", "2020-03-25", "2020-03-26", "2020-03-27"]
count_array=[{date: "2020-03-22", count: 310},
 {date: "2020-03-23", count: 115},
 {date: "2020-03-24", count: 78},
 {date: "2020-03-25", count: 29},
 {date: "2020-03-26", count: 36},
 {date: "2020-03-27", count: 3}]

const countsByDate = Object.fromEntries(
  count_array.map(({ date, count }) => [date, count])
);
const output = date_array.map(date => countsByDate[date] || 0);
console.log(output);