push group result into array mongodb

Question

I have this query in mongodb:

db.getCollection('users').aggregate([
    {
        $group: { 
            _id: "$type",
//             items: { $push: "$_id.type" }
//             items: { $addToSet: "$_id.type" }
        }
    },
    {
        $project: {  
            _id: 0,
            type: "$_id",
        }
    }
]).toArray()

This will return a list like this: [ {type: "AAA"}, {type: "BBB"}, {type: "CCC"} ]

But can I get something like this: ["AAA", "BBB", "CCC"]? Tried with $push and $addToSet but no result. Thank you for your time!

Later edit: You can find an example here: https://mongoplayground.net/p/-n0o5i6CnLq

you can group by null, like this _id: null instead of _id: "$type" — turivishal
– turivishal, Commented Dec 14, 2020 at 18:16
@WernfriedDomscheit I added a link. And the result I want to obtain is ["Male", "Female", "Rather not say", "Other"], an array, not an array of objects — Tenzolinho
– Tenzolinho, Commented Dec 14, 2020 at 18:28

user12582392 · Accepted Answer · 2020-12-14 19:40:04Z

1

Like this?

  {
    $group: {
      _id: null,
      type: {
        $push: "$type"
      }
    }
  },
  {
    $project: {
      _id: 0,
      type: 1
    }
  }

answered Dec 14, 2020 at 19:40

user12582392

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Comments

Wernfried Domscheit · Accepted Answer · 2020-12-14 20:04:16Z

1

Try this one:

db.collection.aggregate([
  {
    $group: {
      _id: null,
      type: {
        "$addToSet": "$type"
      }
    }
  }
])

answered Dec 14, 2020 at 20:04

Wernfried Domscheit

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