[{_id:ObjectId("6d5fc0922982bb550e08502d"),layouts:{nodes:{node1:{x:0,y:0},node2:{x:56,y:24},node3:{x:234,y:34},node4:{x:34,y:15},node5:{x:77,y:12},node6:{x:56,y:42}}}}]

db.collection.aggregate([{$set:{data:{$objectToArray:"$layouts.nodes"}}},{$project:{_id:0,maxX:{$max:"$data.v.x"}}}])