Converting array of objects to array of array

Question

I am new to NoSQL databases and MongoDb. I've got the following question:

I have a collection of such documents:

{
  vals: [
    {
      value: 111,
      timestamp: 1563454669669
    },
    {
      value: 222,
      timestamp: 1563454689665
    },
    {
      value: 333,
      timestamp: 1563454669658
    }
    .......
  ]
}

I would like to convert it into the following documents using aggregation pipeline:

{
  vals: [
    [
      111,
      1563454669669
    ],
    [
      222,
      1563454689665
    ],
    [
      333,
      1563454669658
    ]
    .......
  ]
}

After years of work with relational databases, it's quite hard to understand..

mickl · Accepted Answer · 2019-07-18 13:29:25Z

2

You can use $map operator to transform one array into another array:

db.collection.aggregate([
    {
        $project: {
            vals: {
                $map: {
                    input: "$vals",
                    in: [ "$$this.value", "$$this.timestamp" ]
                }
            }
        }
    }
])

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answered Jul 18, 2019 at 13:29

mickl

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