In mongoDb, how do you remove a array element on specific index position?

Question

In the following example, assume the document is in the db.people collection.

I want to remove an element of index 3 from item list. How can I remove the specific element at index 3?

{
    "_id": "6527c64e539e51befb0db39c",
    "category": "fruits",
    "dataType": "string",
    "isList": true,
    "item": [
        null,
        "mango",
        "banana",
        "kiwi",
        "orange",
        null,
        "watermelon"
    ]
}

This is what I tried:

db.people.update({_id:ObjectId('6527c64e539e51befb0db39c')}, {$unset : {"item.3" : 1 }}) 
db.people.update({_id:ObjectId('6527c64e539e51befb0db39c')}, {$pull : {"item" : null}})

Result I got: It removed all the null values from the item array field.

{
    "_id": "6527c64e539e51befb0db39c",
    "category": "fruits",
    "dataType": "string",
    "isList": true,
    "item": [
        "mango",
        "banana",
        "kiwi",
        "orange",
        "watermelon"
    ]
}

What result I want:

{
    "_id": "6527c64e539e51befb0db39c",
    "category": "fruits",
    "dataType": "string",
    "isList": true,
    "item": [
        null,
        "mango",
        "banana",
        "orange",
        null,
        "watermelon"
    ]
}

Answer 1

Use $slice to get first and later halves of the array before and after the element. Then return it with $concatArrays and $set for the update.

db.collection.update({
  _id: ObjectId("6527c64e539e51befb0db39c")
},
[
  {
    "$set": {
      "item": {
        "$concatArrays": [
          {
            "$slice": [
              "$item",
              3
            ]
          },
          {
            "$slice": [
              "$item",
              4,
              {
                "$size": "$item"
              }
            ]
          }
        ]
      }
    }
  }
])

Mongo Playground