计算嵌套mongodb文档中的出现次数并保留组 [英] Count occurrences in nested mongodb document and keeping group

问题描述

我有这些文件:

[
  {
      "question": 1,
      "answer": "Foo"
  },
  {
      "question": 1,
      "answer": "Foo"
  },
  {
      "question": 1,
      "answer": "Bar"
  },
  {
      "question": 2,
      "answer": "Foo"
  },
  {
      "question": 2,
      "answer": "Foobar"
  }
]

在后端(php)中，我需要获取答案的分区，例如:

And in my backend (php) I need to get the repartition of answers, something like:

• 问题1:

• Question 1:

• "Foo":2/3
• 酒吧":1/3

问题2:

• "Foo":1/2
• "Foobar":1/2

目前，我只想运行mongo查询以实现此结果:

For now I just want to run a mongo query in order to achieve this result:

[
  {
      "question": 1,
      "answers": {
          "Foo": 2,
          "Bar": 1
      }
  },
  {
      "question": 2,
      "answers": {
          "Foo": 1,
          "Foobar": 1
      }
  }
 ]

这是我想出的:

db.getCollection('testAggregate').aggregate([{
    $group: {
        '_id': '$question',
        'answers': {'$push': '$answer'},
    }
}
]);

它返回:

{
    "_id" : 2.0,
    "answers" : [ 
        "Foo", 
        "Foobar"
    ]
},{
    "_id" : 1.0,
    "answers" : [ 
        "Foo", 
        "Foo", 
        "Bar"
    ]
}

现在我需要对Answers字段执行$ group操作以计算出现的次数，但是我需要按问题保留group，但我不知道该怎么做.有人可以帮我吗?

And now I need to to a $group operation on the answers field in order to count the occurences, but I need to keep the group by question and I do not know how to do it. Could someone give me a hand?

推荐答案

您可以使用以下聚合.

按问题和答案分组以获取合并计数，然后按问题分组以获取答案及其计数.

Group by both question and answer to get the count for combination followed by group by question to get the answer and its count.

db.getCollection('testAggregate').aggregate([
  {"$group":{
    "_id":{"question":"$question","answer":"$answer"},
    "count":{"$sum":1}
  }},
  {"$group":{
    "_id":"$_id.question",
    "answers":{"$push":{"answer":"$_id.answer","count":"$count"}}
  }}
]);

您可以使用以下代码在3.4中获取所需的格式.

You can use below code to get the format you want in 3.4.

将$group键更改为k和v，后跟 $addFields 与 $arrayToObject 将数组转换为命名键值对.

Change $group keys into k and v followed by $addFields with $arrayToObject to transform the array into named key value pairs.

db.getCollection('testAggregate').aggregate([
  {"$group":{
    "_id":{"question":"$question","answer":"$answer"},
    "count":{"$sum":1}
  }},
  {"$group":{
    "_id":"$_id.question",
    "answers":{"$push":{"k":"$_id.answer","v":"$count"}}
  }},
 {"$addFields":{"answers":{"$arrayToObject":"$answers"}}}
]);

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