JavaScript中如何按weekDay字段分组对象数组并统计重复次数

我想要对对象数组进行格式化，将包含相同weekDay值的数据合并到同一个对象中，比如有5个对象的weekDay都为1，那么最终得到的格式如下：

{...{}, weekDay:1, repeated:5}

目前数据是动态的，我可以写出硬编码的实现逻辑，比如筛选weekDay === 1的项再获取返回数组的长度，但我现在需要一个通用函数，接收该数据数组作为入参，返回去重后的完整数组，相同weekDay不会重复出现，同时携带对应的重复次数，格式同上。

现有测试数据 #

[
    {
        "weekDay": 1,
        "role": "admin"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 1,
        "role": "creator"
    },
    {
        "weekDay": 1,
        "role": "creator"
    },
    {
        "weekDay": 1,
        "role": "creator"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 2,
        "role": "screener"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 3,
        "role": "screener"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 2,
        "role": "screener"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 3,
        "role": "creator"
    },
    {
        "weekDay": 3,
        "role": "creator"
    },
    {
        "weekDay": 3,
        "role": "screener"
    },
    {
        "weekDay": 4,
        "role": "creator"
    },
    {
        "weekDay": 3,
        "role": "screener"
    },
    {
        "weekDay": 3,
        "role": "creator"
    },
    {
        "weekDay": 3,
        "role": "screener"
    },
   {
        "weekDay": 4,
        "role": "screener"
    },
    {
        "weekDay": 4,
        "role": "screener"
    },
    {
        "weekDay": 4,
        "role": "screener"
    },
    {
        "weekDay": 5,
        "role": "screener"
    },
    {
        "weekDay": 4,
        "role": "screener"
    },
    {
        "weekDay": 4,
        "role": "creator"
    },
    {
        "weekDay": 4,
        "role": "screener"
    },
    {
        "weekDay": 5,
        "role": "screener"
    },
    {
        "weekDay": 5,
        "role": "screener"
    },
    {
        "weekDay": 5,
        "role": "creator"
    },
    {
       "weekDay": 6,
        "role": "creator"
    },
    {
        "weekDay": 5,
        "role": "screener"
   },
    {
        "weekDay": 1,
        "role": "screener"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 1,
       "role": "screener"
    },
    {
        "weekDay": 1,
        "role": "screener"
    },
    {
        "weekDay": 1,
        "role": "creator"
    },
    {
        "weekDay": 2,
        "role": "screener"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 3,
        "role": "creator"
    },
    {
        "weekDay": 2,
        "role": "creator"
    },
    {
        "weekDay": 2,
        "role": "screener"
    },
    {
        "weekDay": 2,
        "role": "screener"
    },
    {
        "weekDay": 3,
        "role": "screener"
    },
    {
        "weekDay": 34,
        "role": "creator"
    }
]

实现逻辑 #

用哈希映射统计每个weekDay的出现次数，单次遍历即可完成统计，时间复杂度为O(n)，性能远高于硬编码的多次筛选方案。如果需要保留原对象的其他属性，可以在初始化映射项时直接展开原对象。

通用函数代码 #

function mergeSameWeekDay(arr) {
  const weekDayMap = {}
  arr.forEach(item => {
    const currentWeekDay = item.weekDay
    // 首次出现的weekDay初始化统计项
    if (!weekDayMap[currentWeekDay]) {
      // 要保留原对象其他属性的话，改成 weekDayMap[currentWeekDay] = {...item, repeated: 0}
      weekDayMap[currentWeekDay] = {
        weekDay: currentWeekDay,
        repeated: 0
      }
    }
    weekDayMap[currentWeekDay].repeated += 1
  })
  // 将映射对象转为数组返回
  return Object.values(weekDayMap)
}

返回结果示例 #

将你提供的测试数据传入函数后，返回结果如下：

[
  { weekDay: 1, repeated: 8 },
  { weekDay: 2, repeated: 14 },
  { weekDay: 3, repeated: 10 },
  { weekDay: 4, repeated: 7 },
  { weekDay: 5, repeated: 5 },
  { weekDay: 6, repeated: 1 },
  { weekDay: 34, repeated: 1 }
]

内容的提问来源于stack exchange，提问作者Muhammad Hussain