MongoDB 对按数组元素分组的数组中的匹配字符串进行计数

如何解决MongoDB 对按数组元素分组的数组中的匹配字符串进行计数

我有一个 MongoDB 集合，用于存储调查的答案。答案通常是带有“优秀”、“良好”或“差”等响应的单选按钮。我正在尝试生成一个查询，该查询为每个问题返回给定响应的总数。响应当前存储在字符串数组中。数组中的位置 0 是问题 1 的答案，依此类推。

我目前有一个聚合查询，它以以下截断格式返回数据：

[{ 
    "name" : "Medical Visit Survey","question" : [
        "Ease of making an appointment?","About how long was your wait time before being seen by the provider?","Professionalism of person who took your call?"
    ],"type" : [ "radiobutton","radiobutton","radiobutton" ],"answers" : [ "Excellent","Less than 20 minutes","Excellent" ]
},{ 
    "name" : "Medical Visit Survey","answers" : ["Excellent","Very Good" ]
}]

产生类似于以下内容的最佳方法是什么：

[{
   "name" : "Medical Visit Survey","question" : "Ease of making an appointment?","type" : "radiobutton","answers": { 
                 "Excellent": 2,"Good": 3,"Poor": 1
              }
  
},{
   "name" : "Medical Visit Survey","question" : "About how long was your wait time before being seen by the provider?","answers": { 
                 "Less than 20 minutes": 2,"More than 20 minutes": 3,"More than 60 minutes": 1
              }
  
}
]

我尝试过类似以下的查询：

[
  {$unwind: "$answers" },{ $group: { _id: "$answers",count: { $sum: 1 } } }
]

输出根据给出的答案对响应进行计数，但不考虑问题编号（数组中的元素位置）。

我有一个可能有用的 mongo playground 链接：https://mongoplayground.net/p/4_uM7khrMEM

如有任何帮助，我们将不胜感激。

解决方法

我不确定有没有最好的方法来做到这一点，但我建议使用一个聚合查询，

• $unwind 解构 question 数组并在问题的每个元素的 index 字段中包含数组索引
• $arrayElemAt 选择提供的 answer 字段的特定 index，type 字段也相同
• $group by question 和 answer，选择必填字段并统计总数
• $group 仅通过 question 并以键值格式构造 answers 数组
• $arrayToObject 将 answers 数组转换为对象

[
  {
    $unwind: {
      path: "$question",includeArrayIndex: "index"
    }
  },{
    $group: {
      _id: {
        question: "$question",answer: { $arrayElemAt: ["$answers","$index"] }
      },name: { $first: "$name" },type: { $first: { $arrayElemAt: ["$type","$index"] } },count: { $sum: 1 }
    }
  },{
    $group: {
      _id: "$_id.question",answers: {
        $push: { k: "$_id.answer",v: "$count" }
      },type: { $first: "$type" }
    }
  },{ $addFields: { answers: { $arrayToObject: "$answers" } } }
]

Playground