[{"sId":"s1","language":"hindi","service":"editing","count":5,},{"sId":"s2","language":"hindi","service":"editing","count":6,},{"sId":"s2","language":"hindi","service":"reading","count":7,},{"sId":"s3","language":"english","service":"reading","count":10,}]

db.collection.aggregate([{"$group":{"_id":{"language":"$language","sId":"$sId"},"count":{"$first":{"$sum":"$count"}}}},{"$group":{"_id":{"language":"$_id.language"},"count":{"$sum":"$count"}}},{"$project":{"_id":0,"language":"$_id.language","count":"$count"}}])