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db.collection.aggregate([{"$group":{"_id":{"$toDate":{"$subtract":[{"$toLong":{$toDate:"$createdAt"}},{"$mod":[{"$toLong":{$toDate:"$createdAt"}},21600000]}]}},count:{$sum:1}}},{$group:{_id:{day:{$dayOfWeek:"$_id"},hour:{$hour:"$_id"}},count:{$sum:"$count"},interval:{$first:"$_id"}}},{$group:{_id:"$_id.day",intervals:{$push:{count:"$count",interval:"$interval"}}}}])