MongoDB: group by day (aggregate)

mongo_group_by_day.js

var mention_id = 620996;

db.mentionStats.aggregate([
    { $match: {'mention_id': mention_id}},
    { $group: {'_id': {
                    'year': { '$year': "$verification_date" },
                    'month': { '$month': "$verification_date" },
                    'day': { '$dayOfMonth': "$verification_date" }
                },
                'retweets': { $last: "$retweets" }}},
    
]).result