Sum all values of same named fields of docs in a collection

Question

I have a database with the following documents:

{ name: \"John\", a: 20, b: 30, c: 40, d: 50  },     
{ name: \"Rich\", a: 20, b: 30, c: 40, d: 50  },      
{ na         


        

Answer 1

You can take advantage of $objectToArray and $arrayToObject operators to dynamically read your object keys. To get rid of _id and name fields you can $filter by $type.

db.collection.aggregate([
    {
        $project: {
            _id: 0,
            fields: {
                $filter: {
                    input: { $objectToArray: "$$ROOT" },
                    cond: { $eq: [ { $type: "$$this.v" }, "double" ] }
                }
            }
        }
    },
    {
        $unwind: "$fields"
    },
    {
        $group: {
            _id: "$fields.k",
            total: { $sum: "$fields.v" }
        }
    },
    {
        $group: {
            _id: null,
            aggregates: { $push: { k: "$_id", v: "$total" } }
        }
    },
    {
        $replaceRoot: {
            newRoot: { $arrayToObject: "$aggregates" }
        }
    }
])

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