获取集合mongodb中所有文档中多个元素的频率 [英] Get frequency for multiple elements in all documents inside a collection mongodb

问题描述

这就是我的问题.

我是mongodb的新手，并且有一个收集文档的集合，如下所示:

  {"_id":{"$ oid":"60626db173b4ca321c02ee3e"；}，年份":"2021"，"name":"Book 1"，作者":["Joe，B"，"Jessica，K"]，"createdAt":{"$ date":"2021-03-30T00:15:45.859Z"}}，{"_id":{"$ oid":"60626db173b4ca321c02ee4e"；}，年份":"2021"，作者":[卡尔，B"，杰西卡，K"]，名称":"Book 2""createdAt":{"$ date":"2021-03-30T00:15:45.859Z"}}， 

我需要了解所有作者的频率和书籍的年代.

期望的结果将是这样的(只要我能获得每个元素的频率，返回结果的方式并不重要)

  {作者":{"Joe，B":1，卡尔，B":1，"Jessica，K":2}，年份":{"2021":2}} 

我已经看到了该线程如何计算每个值都在数组中?在一个数组中完成工作，但是我不知道是否有可能同时获取多个元素(年份，作者)的频率，或者如何做到这一点.>

感谢您的帮助.谢谢.

解决方案

演示- https://mongoplayground.net/p/95JtQEThxvV

$ group ://docs.mongodb.com/manual/reference/operator/aggregation/push/"rel =" nofollow noreferrer> $ push 作者进入数组即可得到 $ group 并获得 $ sum 作者发生的次数

$ group 以null组合所有文档，请使用 $ addToSet 推送唯一值并转换 $ first

  db.collection.aggregate([{$ group:{_id:{year:"$ year"}，作者:{$ push:" $ authors"}，yearCount:{$ sum:1}}}，{$ unwind:" $ authors"}，{$ unwind:" $ authors"}}，{$ group:{_id:{author:" $ authors"}，年:{$ first:" $ _ id.year"}，yearCount:{$ first:"$ yearCount"}，作者:{$ push:" $ authors"}，authorCount:{$ sum:1}}}，{"$ group":{_id:null，年: {$ addToSet:{k:"$ year"，v:"$ yearCount"；}}，作者:{$ addToSet:{k:"$ _ id.author"，v:"$ authorCount"；}}}}，{$ project:{_id:0，年:{$ arrayToObject:" $ years"}，作者:{$ arrayToObject:" $ authors"}}}]) 

演示2-按年份分组的作者数- https://mongoplayground.net/p/_elnjmknroF

So heres my problem.

I am new to mongodb and have a collection which documents are saved like this:

{
 "_id": {
    "$oid": "60626db173b4ca321c02ee3e"
 },
 "year": "2021",
 "name": "Book 1",
 "authors": ["Joe, B", "Jessica, K"],
 "createdAt": {
     "$date": "2021-03-30T00:15:45.859Z"
 }
},
{
 "_id": {
    "$oid": "60626db173b4ca321c02ee4e"
 },
 "year": "2021",
 "authors": ["Carl, B", "Jessica, K"],
 "name": "Book 2"
 "createdAt": {
     "$date": "2021-03-30T00:15:45.859Z"
 }
},

I need to get both the frequency of all authors and the years of the books.

The expected result would be something like this (as long as i can get each element frequency it doesn't really matter how the results are returned):

{
  "authors": {
     "Joe, B": 1,
     "Carl, B": 1,
     "Jessica, K": 2
  },
  "year": {
     "2021": 2
  }
}

I've seen this thread How to count occurence of each value in array? which does the job in one array but i have no idea if its possible to adapt to get the frequency of multiple elements (year, authors) at the same time or how to do it.

I appreciate any help. Thank you.

解决方案

Demo - https://mongoplayground.net/p/95JtQEThxvV

$group by year $push authors into the array get $sum count of the year occurrence, $unwind into individuals documents.

$group by authors and get $sum count of the author occurrence

$group by null to combine all documents, use $addToSet to push unique values and convert $arrayToObject to get final output in $project

$first

db.collection.aggregate([
  {
    $group: {
      _id: { year: "$year" },
      authors: { $push: "$authors" },
      yearCount: { $sum: 1 }
    }
  },
  { $unwind: "$authors" },
  { $unwind: "$authors"},
  {
    $group: {
      _id: { author: "$authors" },
      year: { $first: "$_id.year" },
      yearCount: { $first: "$yearCount" },
      authors: { $push: "$authors" },
      authorCount: { $sum: 1 }
    }
  },
  {
    "$group": {
      _id: null,
      years: {
        $addToSet: { k: "$year", v: "$yearCount" }
      },
      authors: {
        $addToSet: { k: "$_id.author", v: "$authorCount" }
      }
    }
  },
  {
    $project: {
      _id: 0,
      years: { $arrayToObject: "$years" },
      authors: { $arrayToObject: "$authors" }
    }
  }
])

Demo 2 - For author count grouped by year- https://mongoplayground.net/p/_elnjmknroF

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