How to include $sum field for each existing field in a document with aggregate?

Question

I have this document.

{
"_id": "1",
"name": "KP",
"points": 20
},
{
"_id": "2",
"name": "Josh",
"points: 30
}, 
{
"_id": "3",
"name": "Angelo",
"points": 50
}

How do I get the sum of all fields (should be 100) and then add them on each document?

{
"_id": "1",
"name": "KP",
"points": 20,
"total": 100
},
{
"_id": "2",
"name": "Josh",
"points": 30,
"total": 100
}, 
{
"_id": "3",
"name": "Angelo",
"points": 50,
"total": 100
}

I need this so I could divide and multiply later on because my plan really is to add a percent field, like a share on the total points (i.e. for 50 pts, (50 / 100) * 100 = 50%. Like this:

{
"_id": "1",
"name": "KP",
"points": 20,
"percentage": 20
},
{
"_id": "2",
"name": "Josh",
"points": 30,
"total": 30
}, 
{
"_id": "3",
"name": "Angelo",
"points": 50,
"percentage": 50
}

So far I have this which is incorrect:

db.users.aggregate({$match:{}}, {$project: {_id: 1, name: 1, points: "$points"}}, {$group: {_id: "$name", total: {$sum: "$points"}}})

Answer 1

Use $setWindowFields to compute the total with "partitionBy": null. Then use $divide and $multiply to compute the percentage.

db.collection.aggregate([
  {
    "$setWindowFields": {
      "output": {
        "total": {
          "$sum": "$points"
        }
      }
    }
  },
  {
    $set: {
      percentage: {
        "$multiply": [
          {
            "$divide": [
              "$points",
              "$total"
            ]
          },
          100
        ]
      }
    }
  }
])

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