[{name:"bob",number:20},{name:"bob",number:10},{name:"kol",number:20},{name:"bob",number:10},{name:"kol",number:10},]

db.collection.aggregate([{$sort:{number:1}},{$group:{_id:"$name",number:{$push:"$number"}}},{$project:{name:"$_id",number:{$setIntersection:["$number"]},_id:0}},{$sort:{name:1}}])