[{"Pharmacy":"a","EstablishedDate":ISODate("2006-10-12"),"Medicine":[{"MedName":"MedA","Quantity":55},{"MedName":"MedB","Quantity":34},{"MedName":"MedD","Quantity":25}]},{"Pharmacy":"b","EstablishedDate":ISODate("2015-02-02"),"Medicine":[{"MedName":"MedB","Quantity":60},{"MedName":"MedC","Quantity":34}]}]

db.collection.aggregate([{$unwind:"$Medicine"},{$sort:{EstablishedDate:-1}},{$group:{_id:"$Medicine.MedName",Pharmacy:{$first:"$Pharmacy"}}},{$project:{_id:0,"Medicine":"$_id","Pharmacy":"$Pharmacy"}}])