Using $trunc in a pipeline

Working with Data
1

Hello,
I have written the following code

db.movies.aggregate([
  {
    $match: {
      languages: "English"
    }
  },
  {
    $unwind: "$cast"
  },
  {
    $group: {
      _id: "$cast",
      numFilms: {
        $sum: 1
      },
      average : {
       $avg : "$imdb.rating"
      }
    }
  },
 {
    $sort: {
      numFilms: -1,
      average: -1
    }
  }
])

And I would like to display the truncated average, but $tunc can not be used inside $group, how can I solve this?

Thanks

2

You could use https://docs.mongodb.com/manual/reference/operator/aggregation/addFields/ after $group to truncate the value of the field average.