Database
[{"name":"b1","y2000":80,"y2001":105},{"name":"b1","y2000":80,"y2001":105},{"name":"b2","y2000":80,"y2001":105},{"name":"b3",},{"name":"b4","y2000":80},{"name":"b5","y2001":80}]
Query
db.collection.aggregate([{$match:{"y2000":{$exists:true},"y2001":{$exists:true}}},{$group:{_id:"$name",y2000:{$sum:"$y2000"},y2001:{$sum:"$y2001"}}},{$project:{_id:0,x:"$_id",y2000:1,y2001:1}}])