Mongodb 按列表中的元素和字段计数

我有一个MongoDB集合，看起来像这样：

{ "_id" : 1, "owner" : "Alice", airline: "RSAirlines", "content" : ["shoes", "pants", "sockets"]}
{ "_id" : 2, "owner" : "Bob", airline: "RSAirlines", "content" : ["phone", "pants"]}
{ "_id" : 3, "owner" : "Charlie", airline: "RSAirlines", "content" : ["shoes", "pants", "bag"]}
{ "_id" : 4, "owner" : "Mary" ,airline: "AirES" "content" : ["sandals", "coins", "sockets"]}
{ "_id" : 5, "owner" : "Olivia", airline: "AirES", "content" : ["gloves", "pants", "sockets"]}
{ "_id" : 6, "owner" : "Dan", airline: "AirES", "content" : ["sockets", "wallet"]}
{ "_id" : 7, "owner" : "Erin", airline: "AirES", "content" : ["pants", "sockets", "dress"]}

我想对它们进行

聚合

以获得以下结果：

{ "_id": "RSAirlines", "counts": {
    "shoes": 2,
    "pants": 3,
    "sockets": 1,
    "phone": 1,
    "bag": 1
}}
{ "_id": "AirES", "counts": {
    "sandals": 1,
    "coins": 1,
    "sockets": 4,
    "wallet": 1,
    "dress": 1,
   "pants": 2
}}

以前我看到过计算元素的方法，但现在我想按

航空公司

• $unwind

  解构

  内容

  数组

• $group

  通过

  航空公司和
  内容获取总计数

• $组

  由唯一的

  航空公司

  和构造

  计数

  数组键值格式

• $arrayToObject

  将键值数组转换为对象

---

如果我想要每个内容的顶部

n

？你能举个例子吗，我没有得到确切的答案。就像前2个一样，它会输出：

{id:“RSAirlines”，“counts:{“shoes”：2，“pants”：3，}{{id:“AirES”，“counts:{“sockets”：4，“pants”：2}{/code>看到了吗，您可以使用$sort by count和$slice来选择元素的数量。是的，这就是我要找的，谢谢
db.collection.aggregate([
  { $unwind: "$content" },
  {
    $group: {
      _id: {
        airline: "$airline",
        content: "$content"
      },
      count: { $sum: 1 }
    }
  },
  {
    $group: {
      _id: "$_id.airline",
      counts: {
        $push: {
          k: "$_id.content",
          v: "$count"
        }
      }
    }
  },
  { $project: { counts: { $arrayToObject: "$counts" } } }
])