MongoDB - How to remove part of field with $unset

Question

I have a database in MongoDB where there are entries with the following structure image

I am using a script in Python that I use to retrive information from this strucutre and then saves it to a csv.

The end goal is to remove ONLY SOME parts of the parameters structure. For instance, I want to keep parameters[0].values and parameters[1].values but not parameters[2:5].values

I am not experienced in this but the command I am using is the following

{"$unset":"exercises.parameters.values"] }

but this will remove all values from all the objects inside parameters. Since the variable has the same name amongst the objects I can't find a way to specify which ones I want.

I have also tried indexing like so

{"$unset":"exercises.parameters[2].values"] }

but that doesn't seem to work...

Help is much appreciated!

Answer 1

update

db.collection.update({
  "_id": 1
},
{
  "$unset": {
    "exercises.$[].parameters.2.values": "",
    "exercises.$[].parameters.3.values": "",
    "exercises.$[].parameters.4.values": "",
    "exercises.$[].parameters.5.values": ""
  }
},
{
  "multi": true
})

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---

aggregate

db.collection.aggregate([
  {
    $set: {
      "exercises": {
        "$map": {
          "input": "$exercises",
          "as": "item",
          "in": {
            "$mergeObjects": [
              "$$item",
              {
                parameters: {
                  $slice: [ "$$item.parameters", 2 ]
                }
              }
            ]
          }
        }
      }
    }
  }
])

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