Grouping within arraythen converting it to object

[Sreekanth_R_Shekar]

@Rafael_Green

db.collection.aggregate(
[{
    $addFields: {
        students: {
            $function: {
                body: function(students) {
                    let retVal = {};
                    for (let student of students) {
                        if (!retVal[student.name]) {
                            retVal[student.name] = []
                        }
                        retVal[student.name].push(student.grade)
                    }
                    return retVal;
                },
                args: ["$students"],
                lang: "js"
            }
        },
    }
}])

Thank you, but my version is mongoDB 4.2.8 and hence I cannot use “$function”. Is there any workaround for this?