Mongodb 如何在mongo中计算数组元素

我知道有很多话题都在谈论这一点，但我不知道我的实现中出现了什么问题

我有以下文件：

{
  "_id" : ObjectId("510a353929e16756d5000009"),
  "skills" : [
    [
      "UserEmbed::Author::Skills::Copywriting",
      "UserEmbed::Author::Skills::Proofreading",
      "UserEmbed::Author::Skills::Proofreading",
      "UserEmbed::Author::Skills::Translation",
      "UserEmbed::Author::Skills::Translation",
      "UserEmbed::Author::Skills::Translation"
    ]
  ]
}

{
  "_id" : [
    "UserEmbed::Author::Skills::Copywriting",
    "UserEmbed::Author::Skills::Copywriting",
    "UserEmbed::Author::Skills::Copywriting",
    "UserEmbed::Author::Skills::Translation",
    "UserEmbed::Author::Skills::Translation",
    "UserEmbed::Author::Skills::Translation"
  ],
  "count" : 1
}

我想要这样的东西：

{
  "UserEmbed::Author::Skills::Copywriting": 1,    
  "UserEmbed::Author::Skills::Proofreading": 2,
  "UserEmbed::Author::Skills::Translation": 3
}

以下是我所拥有的（第一个

$group

是从我的原始文档结构中获取上面的文档）：

返回如下内容（与其他文档一起）：

---

似乎

$组

工作不正常。我误解了什么吗？

鉴于您的文档包含数组，您需要为

$skills

引入第二个

$unwind

：

db.so.aggregate([
    { $group: { _id: "$_id", 
        skills: { $addToSet : "$author_profile.skills._type" }}},
    { $unwind : "$skills" }, 
    { $unwind: "$skills" },
    { $group : { _id : "$skills", count: { $sum : 1 } } }])

产生：

"result" : [
        {
            "_id" : "UserEmbed::Author::Skills::Translation",
            "count" : 3
        },
        {
            "_id" : "UserEmbed::Author::Skills::Proofreading",
            "count" : 2
        },
        {
            "_id" : "UserEmbed::Author::Skills::Copywriting",
            "count" : 1
        }
    ],
"ok" : 1

---

你知道我如何按照第一个id对结果进行分组吗？我不明白你的意思。。。按

\u id

分组？我算出了，想按初始

\u id

分组。那是不是

\u id:{user\u id:$\u id'，键入：$skills}

"result" : [
        {
            "_id" : "UserEmbed::Author::Skills::Translation",
            "count" : 3
        },
        {
            "_id" : "UserEmbed::Author::Skills::Proofreading",
            "count" : 2
        },
        {
            "_id" : "UserEmbed::Author::Skills::Copywriting",
            "count" : 1
        }
    ],
"ok" : 1