[{qClass:[{cat:"Servers",class:"High Impact Maintenance",total:1},{cat:"Network.TrafficShapers",class:"Maintenance",total:16},{cat:"Network.Hop",class:"Core Failure",total:2},{cat:"Office.MFD",class:"Failure",total:4},{cat:"Office.Printers",class:"Maintenance",total:36},{cat:"Office.MFD",class:"Maintenance",total:880},{cat:"Network.TrafficShapers",class:"Failure",total:47},{cat:"Servers",class:"Core Maintenance",total:1},{cat:"Network.Switches",class:"Failure",total:5},{cat:"Servers",class:"Performance",total:21},{cat:"Network.Switches",class:"High Impact Failure",total:4},{cat:"Network.Firewall",class:"Core Failure",total:2},{cat:"Network.Router",class:"Failure",total:53},{cat:"Servers",class:"High Impact Failure",total:3},{cat:"Office.Printers",class:"Performance",total:1},{cat:"Network.TrafficShapers",class:"Performance",total:3},{cat:"Network.Switches",class:"Maintenance",total:1},{cat:"Servers",class:"Failure",total:60},{cat:"Network.Router",class:"Performance",total:67},{cat:"Network.Router",class:"High Impact Failure",total:39},{cat:"Office.MFD",class:"Performance",total:5},{cat:"Network.TrafficShapers",class:"High Impact Failure",total:593},{cat:"Network.Router",class:"Maintenance",total:78},{cat:"Office.Printers",class:"High Impact Failure",total:2},{cat:"Office.Printers",class:"Failure",total:1},{cat:"Office.MFD",class:"Critical Failure",total:48}]}]

db.collection.aggregate([{$unwind:"$qClass"},{$group:{_id:"$qClass.cat",cat:{$first:"$qClass.cat"},classes:{$push:{k:"$qClass.class",v:"$qClass.total"}},total:{$sum:"$qClass.total"}}},{$replaceRoot:{newRoot:{$mergeObjects:["$$ROOT",{$arrayToObject:"$classes"}]}}},{$project:{_id:0,classes:0}}])