[{"_id":1,"achievements":{"third_record":true,"second_record":true}},{"_id":3,"achievements":{"sixth_record":true,"second_record":true}},{"_id":2,"achievements":{"first_record":true,"fifth_record":true}},{"_id":4,"achievements":{"first_record":true,"second_record":true}},]

db.collection.aggregate([{$project:{as:{$objectToArray:"$achievements"}}},{$unwind:"$as"},{$group:{_id:"$as.k",number:{$sum:{"$cond":[{$eq:["$as.v",true]},1,0]}}}}])