Database
[{count:1,status:"FAILED",article_id:1},{count:1,status:"DELIVERED",article_id:1}]
Query
db.collection.aggregate([{$group:{_id:"$article_id",FAILED:{"$sum":{"$cond":[{"$eq":["$status","FAILED"]},1,0]}},DELIVERED:{"$sum":{"$cond":[{"$eq":["$status","DELIVERED"]},1,0]}}}}])