How to convert an array to object by mongoDB aggregate

Question

Using a MongoDB aggregate query, how do I convert an array of documents to a single document. The array can have N number of documents.

Before

{
    "_id": "10217941",
    "data": [
    {
        "count": 2,
        "score": "0.5"
    },
    {
        "count": 6,
        "score": "0.3"
    },
    {
        "count": 5,
        "score": "0.8"
    }
    ]
}

After

"_id": "10217941",
"0.3": 6,
"0.5": 2,
"0.8": 5

Use $arrayToObject

Arsen Davtyan
– Arsen Davtyan

2019-12-26 08:27:02 +00:00
Commented Dec 26, 2019 at 8:27 — Arsen Davtyan
– Arsen Davtyan, Commented Dec 26, 2019 at 8:27

Tom Slabbaert · Accepted Answer · 2019-12-26 08:33:39Z

1

Try this:

db.collection.aggregate([
    {
        "$addFields": {
            "data": {
                "$arrayToObject": {
                    "$map": {
                        "input": "$data",
                        "as": "item",
                        "in": {
                            "k": "$$item.score",
                            "v": "$$item.count"
                        }
                    }
                }
            }
        }
    },
    {
        "$addFields": {
            "data._id": "$_id"
        }
    },
    {
        "$replaceRoot": {
            "newRoot": "$data"
        }
    }
]);

answered Dec 26, 2019 at 8:33

Tom Slabbaert

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