基于roomId合并嵌套数组并统计日期频次的实现咨询

问题描述 #

现有一组包含roomId与nights数组的对象，需根据roomId合并同一ID对应的nights数组，同时统计每个日期的出现频次。尝试过map、reduce函数但未得到预期结果，寻求解决方案。

输入示例 #

const data = [
  {roomId: 1,
   nights: [ "2022-05-06",
             "2022-05-07"
           ] 
  },
  {roomId: 2,
   nights: [ "2022-05-06",
             "2022-05-07",
             "2022-05-08"
           ] 
  },
  {roomId: 1,
   nights: [ "2022-05-10",
             "2022-05-11",
             "2022-05-07",
           ] 
  },
  {roomId: 2,
   nights: [ "2022-05-12",
             "2022-05-13",
             "2022-05-14"
           ] 
   }
];

期望输出 #

const newObject = [
  {roomId: 1,
   nights: [ {date:"2022-05-06", count:1},
             {date:"2022-05-07", count:2},
             {date:"2022-05-10", count:1},
             {date:"2022-05-11", count:1}
           ] 
  },
  {roomId: 2,
   nights: [ {date:"2022-05-06",count:1},
             {date:"2022-05-07",count:1},
             {date:"2022-05-08",count:1},
             {date:"2022-05-12",count:1},
             {date:"2022-05-13",count:1},
             {date:"2022-05-14",count:1}
           ] 
  },
];

解决方案 #

可以通过两次reduce配合map实现需求，分两步完成：

1. 按roomId分组，合并同一房间的所有日期数组
2. 对每个房间的日期数组统计频次，转换为目标格式

具体代码如下：

const data = [
  {roomId: 1, nights: ["2022-05-06", "2022-05-07"]},
  {roomId: 2, nights: ["2022-05-06", "2022-05-07", "2022-05-08"]},
  {roomId: 1, nights: ["2022-05-10", "2022-05-11", "2022-05-07"]},
  {roomId: 2, nights: ["2022-05-12", "2022-05-13", "2022-05-14"]}
];

// 第一步：按roomId分组，合并所有日期
const groupedRooms = data.reduce((acc, current) => {
  const existingRoom = acc.find(room => room.roomId === current.roomId);
  if (existingRoom) {
    existingRoom.nights.push(...current.nights);
  } else {
    acc.push({...current});
  }
  return acc;
}, []);

// 第二步：统计每个日期的出现次数并转换格式
const result = groupedRooms.map(room => {
  const dateCountMap = room.nights.reduce((map, date) => {
    map[date] = (map[date] || 0) + 1;
    return map;
  }, {});
  return {
    roomId: room.roomId,
    nights: Object.entries(dateCountMap).map(([date, count]) => ({date, count}))
  };
});

console.log(result);

代码说明 #

• 第一阶段的reduce遍历原始数据，将相同roomId的对象合并，把所有nights数组拼接成一个包含该房间所有日期的数组。
• 第二阶段先通过reduce生成日期到频次的映射对象，再用Object.entries将映射转换为{date, count}格式的数组，最终得到符合要求的结构。

内容的提问来源于stack exchange，提问作者Code4fun