mongodb - MongoDB 聚合，用于将值重塑或分组为字段名称和月份

Question

我的数据格式为：

 [{ _id: 1, Prom: "I", date: ISOdate(2016-01-01 ... ) },
  { _id: 2, Prom: "P", date: ISOdate(2016-01-01 ... ) },
  { _id: 3, Prom: "D", date: ISOdate(2016-02-01 ... ) },
  { _id: 4, Prom: "I", date: ISOdate(2016-03-01 ... ) },
  { _id: 5, Prom: "I", date: ISOdate(2016-04-01 ... ) },
  { _id: 6, Prom: "D", date: ISOdate(2016-04-01 ... ) },
  { _id: 7, Prom: "P", date: ISOdate(2016-04-01 ... ) },
  ...
  { _id: 512, Prom: "I", date: ISOdate(2016-04-01 ... ) },
  { _id: 632, Prom: "P", date: ISOdate(2016-06-01 ... ) },
  { _id: 656, Prom: "I", date: ISOdate(2016-06-01 ... ) }]

然后我汇总数据以计算每月“P”、“I”或“D”的数量，如下所示：

db.Collection.aggregate([
{
  $group: {
      _id: { Mnt:"$Mnt", Prom: "$Prom"} ,
      Count: {$sum: 1 },
  }
 }
]);

这给了我结果：

 [{ "_id" : { "Mnt" : { "$date" : "2016-01-01T00:00:00.000+0000" }, "Prom" : "D" }, "Count" : 32 }
 { "_id" : { "Mnt" : { "$date" : "2016-01-01T00:00:00.000+0000" }, "Prom" : "P" }, "Count" : 138 }
 { "_id" : { "Mnt" : { "$date" : "2016-01-01T00:00:00.000+0000" }, "Prom" : "I" }, "Count" : 178 }
 { "_id" : { "Mnt" : { "$date" : "2016-02-01T00:00:00.000+0000" }, "Prom" : "D" }, "Count" : 46 }
 { "_id" : { "Mnt" : { "$date" : "2016-02-01T00:00:00.000+0000" }, "Prom" : "P" }, "Count" : 287 }
 { "_id" : { "Mnt" : { "$date" : "2016-02-01T00:00:00.000+0000" }, "Prom" : "I" }, "Count" : 197 }
  ....
 { "_id" : { "Mnt" : { "$date" : "2016-06-01T00:00:00.000+0000" }, "Prom" : "D" }, "Count" : 55 }
 { "_id" : { "Mnt" : { "$date" : "2016-06-01T00:00:00.000+0000" }, "Prom" : "P" }, "Count" : 42 }
 { "_id" : { "Mnt" : { "$date" : "2016-06-01T00:00:00.000+0000" }, "Prom" : "I" }, "Count" : 14 }]

如何对这些数据进行分组或投影，以格式表示我的数据？

[{ Mnt: ISOdate(2016-01-01 ...), "P": 138, "I": 178, "D": 32 },
 { Mnt: ISOdate(2016-02-01 ...), "P": 287, "I": 197, "D": 46 },
 ...
 { Mnt: ISOdate(2016-06-01 ...), "P": 42, "I": 14, "D": 55 }]

我真的没有找到一种方法来使用“Prom”的值作为管道中下一个聚合的键。按月分组这个结果也是有问题的。本质上，我们想要做的是按月从原始数据中创建一个净推荐值，其中 P - 推荐者，D - 批评者，I - 无动于衷。

Answer 1

尝试这个，

 db.Collection.aggregate([
    {
      $group: {
          _id: { Mnt:"$Mnt", Prom: "$Prom"} ,
          Count: {$sum: 1 },
      },
    $group: {
          _id:"$Mnt" ,res: { $push: "$Prom" }      
      },
    $project : { Mnt:$_id , res[0],res[1],res[2]

    }
     }
    ]);