数组数组求和

Question

I would like to find a total based on two arrays pbd and input . The pipeline should multiply the pbd.charge.sellRate with the input.quantity whenever the type and size matches. Also I would like to add all this together to get one grand total.

The input would be

  {
    "pbd": [
      {
        "type": "STD",
        "size": "20",
        "charge": {
          "sellRate": 120
        }
      },
      {
        "containerType": "STD",
        "containerSize": "40",
        "charge": {
          "sellRate": 290
        }
      }
    ],
    "input": [
      {
        "type": "STD",
        "size": "20",
        "quantity": "20"
      },
      {
        "type": "STD",
        "size": "40",
        "quantity": "20"
      }
    ]
  }

So far I've used two $map operators somewhat like two for loops like this:

db.collection.aggregate([
  {
    $project: {
      "grandTotal": {
        $map: {
          input: "$pbd",
          as: "pbd",
          in: {
            $map: {
              input: "$input",
              as: "inp",
              in: {
                $cond: {
                  if: {
                    $and: [
                      {
                        $eq: [
                          "$$pbd.type",
                          "$$inp.type"
                        ]
                      },
                      {
                        $eq: [
                          "$$pbd.size",
                          "$$inp.size"
                        ]
                      }
                    ]
                  },
                  then: {
                    $multiply: [
                      {
                        $toInt: "$$pbd.charge.sellRate"
                      },
                      {
                        $toInt: "$$inp.quantity"
                      }
                    ]
                  },
                  else: 0
                }
              }
            }
          }
        }
      }
    }
  }
])

and the output I get is this

  {
    "_id": ObjectId("5a934e000102030405000000"),
    "grandTotal": [
      [
        2400,
        0
      ],
      [
        0,
        0
      ]
    ]
  }

Now I want to add all this array of arrays to get one total. A better solution to this problem would also be highly appreciated.

This is a part of quite a long aggregation pipeline with lots of other data so I would prefer to not unwind and group the data. Is there any other option?

Answer 1

You can run $reduce as the next step in your pipeline:

db.collection.aggregate([
    // your current aggregation pipeline
    {
        $project: {
            total: {
                $reduce: {
                    input: "$grandTotal",
                    initialValue: 0,
                    in: {
                        $add: [ "$$value", { $sum: "$$this" } ]
                    }
                }
            }
        }
    }
])

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