Whats the best way to aggregate for grouping by particular key and adding the values?

I have a collection in my mongodb named events. Here are few data from it:

[{
  _id: 100,
  streamer_id: a01,
  viewers: 4,
  title: "Event 1"
},{
  _id: 101,
  streamer_id: a01,
  viewers: 7,
  title: "Event 2"
},
{
  _id: 103,
  streamer_id: a02,
  viewers: 3,
  title: "Stream"
},

I basically want the streamer_id to be grouped and the number of viewers to be added. What’s the best way to do it with aggregation?

Havent tried anything yet cause I have no clue how to proceed with this. But this is what I expect:

[{
  _id: any id,
  streamer_id: a01,
  total_viewers: 11
},{
  _id: any id,
  streamer_id: a02,
  total_viewers: 3
},

>Solution :

Please attempt the problem first in future.

But here is a simple approach with $group and $sum. You can also use $project to format your documents as you would like it to be.

Working example: https://mongoplayground.net/p/Ucb2EWgC_Y5

Query:

db.collection.aggregate([
  {
    $group: {
      _id: {
        streamer_id: "$streamer_id",
      },
      total_viewers: {
        $sum: "$viewers"
      }
    }
  },
  {
    $project: {
      _id: 0,
      streamer_id: "$_id.streamer_id",
      total_viewers: 1
    }
  }
])

Result:

[
  {
    "streamer_id": "a01",
    "total_viewers": 11
  },
  {
    "streamer_id": "a02",
    "total_viewers": 3
  }
]