如何获得 objects 不同的两个值的平均值？

Question

我的数据如下：

[
  {
    "_id": ObjectId("6213baa5a013b7c5f1232e23"),
    "birthDate": ISODate("1973-05-01T13:30:15Z"),
    "surname": "Johnson",
    "name": "Emma",
    "registerDate": ISODate("1900-06-11T17:30:15Z"),
    "children": [
      {
        "birthDate": ISODate("1993-05-21T16:30:15Z"),
        "surname": "Johnson",
        "name": "Liam"
      },
      {
        "birthDate": ISODate("1994-01-21T15:30:15Z"),
        "surname": "Johnson",
        "name": "Olivia",
        "registerDate": ISODate("2019-09-14T12:30:15Z")
      }
    ],
    "city": "Houston"
  }
]

我想计算具有 registerDate 的人的注册年龄。在这个例子中，我应该得到 Emma(parent) 和 Olivia(child) 的平均注册年龄。我试过了this。我计算了注册年龄并将它们添加为一个字段。我得到了奥利维亚的注册年龄。但是，我有艾玛的重复注册年龄。我想使用其中之一。我怎样才能得到属于艾玛和奥利维亚的平均注册年龄。我的意思是 (5+1)/2=3。您可以在添加的 link 中看到这些值。

Answer 1

你可以先用$map得到ages数组。然后使用 $avg 得到平均年龄。

$avg ignores non-numeric values, including missing values. If all of the operands for the average are non-numeric, $avg returns null since the average of zero values is undefined.

[
  {
    "$addFields": {
      "ages": {
        "$map": {
          "input": "$children",
          "as": "child",
          "in": {
            $dateDiff: {
              startDate: "$$child.registerDate",
              endDate: "$$NOW",
              unit: "year"
            }
          }
        }
      }
    }
  },
  {
    "$addFields": {
      averageAge: {
        "$avg": {
          "$concatArrays": [
            "$ages",
            [
              {
                $dateDiff: {
                  startDate: "$registerDate",
                  endDate: "$$NOW",
                  unit: "year"
                }
              }
            ]
          ]
        }
      }
    }
  }
]

Mongo playground

如何获得 objects 不同的两个值的平均值？

How to get average of two values which are in different objects?

mongodb

aggregation-framework