MongoDB run loop to add incremental index value in array

I have a MongoDB collection where I have an array of objects and I want to add an incremental index value to each element of the array of objects.


Like index starts from 0 to array length - 1.
db.collection.aggregate([
{
"$unwind": "$array"
},
{
"$addFields": {
"array.index": {
"$add": [
{
"$ifNull": ["$index", 0]
},
1
]
}
}
},
{
"$group": {
"_id": "$_id",
"array": {
"$push": "$$ROOT.array"
}
}
}
])