MongoDB Adding Custom field in aggregate

so here’s my collection. This consists of users and their data

{
  userId: 6udg,
    data: [
       {
        date: 22-09-2022
        hits: 98
       },
      {
       date: 23-09-2022
       hits: 88
      },
      {
       date: 24-09-2022
       hits: 100
      },
      {
       date: 24-11-2022
       hits: 145
      },
      {
       date: 25-11-2022
       hits: 75
      }            
     ]
 },
{
  userId:  7tu5,
    data: [
       {
        date: 22-09-2022
        hits: 98
       },
      {
       date: 23-09-2022
       hits: 88
      },
      {
       date: 24-09-2022
       hits: 100
      },
      {
       date: 24-11-2022
       hits: 18
      },
      {
       date: 25-11-2022
       hits: 65
      }           
     ]
}

Here’s how I’m creating an aggregate with objects for hits filtered by week, month and year. First I match the user whose data we want to fetch. Then I use projection to get the custom fields that I want.

Users.aggregate([
                    {
                        $match: {
                            userId: req.params.userId
                        }
                    },
                    {
                        $project: {
                            _id: 0,
                            last_seven_days: {
                                $filter: {
                                    input: "$data",
                                    as: "index", 
                                    cond: {
                                        $and: [
                                            {
                                                $gte: [
                                                    "$$index.date",
                                                    new Date(moment().utc().startOf("week"))
                                                ]
                                            },
                                            {
                                                $lte: [
                                                    "$$index.date",
                                                    new Date(moment().utc().endOf("week"))
                                                ]
                                            }
                                        ]
                                    }
                                },
                            },
                            last_month: {
                                $filter: {
                                    input: "$data",
                                    as: "index", 
                                    cond: {
                                        $and: [
                                            {
                                                $gte: [
                                                    "$$index.date",
                                                    new Date(moment().utc().startOf("month"))
                                                ]
                                            },
                                            {
                                                $lte: [
                                                    "$$index.date",
                                                    new Date(moment().utc().endOf("month"))
                                                ]
                                            }
                                        ]
                                    }
                                }
                            },
                            last_year: {
                                $filter: {
                                    input: "$data",
                                    as: "index",
                                    cond: {
                                        $and: [
                                            {
                                                $gte: [
                                                    "$$index.date",
                                                    new Date(moment().utc().startOf("year"))
                                                ]
                                            },
                                            {
                                                $lte: [
                                                    "$$index.date",
                                                    new Date(moment().utc().endOf("month"))
                                                ]
                                            }
                                        ]
                                    }
                                }
                            }
                        }
                    }
                ])
 

what I want to do is add a key called ‘average’ in each last_seven_days , last_month, and last_year – containing the average hits for week, month and year respectively

Expected output:

{
   userId: 6udg
   last_seven_day:[ 
           avg: <avg>
           data:[
                 {
                   date:  24-11-2022,
                   hits: 145,
                 },
                 {
                   date:  25-11-2022,
                   hits: 75,
                 }
               ]
             ]
     }