MongoDB. How to combine document with other documents values in aggregation framework?

Question

I have documents like this:

[
  { id: 1, number: 10 },
  { id: 2, number: 11 },
  { id: 3, number: 12 }
]

How to get documents with combination of other values like example below using aggregation framework?

[
  { id: 1, number: 10, other_numbers: [11, 12] },
  { id: 2, number: 11, other_numbers: [10, 12] },
  { id: 3, number: 12, other_numbers: [10, 11] }
]

Answer 1

db.collection.aggregate([
  {
    $lookup: {
      "from": "collection",
      "let": {
        "number": "$number"
      },
      pipeline: [
        {
          $match: {
            $expr: {
              $ne: [ "$number", "$$number" ]
            }
          }
        }
      ],
      "as": "other_numbers"
    }
  },
  {
    $set: {
      "other_numbers": "$other_numbers.number"
    }
  }
])

mongoplayground

---

db.collection.aggregate([
  {
    "$group": {
      "_id": null,
      "number": {
        "$push": "$$ROOT"
      },
      "other_numbers": {
        "$push": "$$ROOT"
      }
    }
  },
  {
    "$unwind": "$number"
  },
  {
    "$set": {
      "other_numbers": {
        "$filter": {
          "input": "$other_numbers.number",
          "as": "i",
          "cond": {
            "$ne": [
              "$$i",
              "$number.number"
            ]
          }
        }
      },
      "number": "$number.number",
      "_id": "$number.id"
    }
  }
])

mongoplayground