Database
[{"_id":"set1","data":{"IND":{"2015-01":0.6753404,"2015-02":1.0502269,"2015-03":1.0902269},"AUS":{"2015-01":0.6753404,"2015-02":1.0502269,"2015-03":1.0902269},"IND_123":{"2015-01":0.6753404,"2015-02":1.0502269,"2015-03":1.0902269}}}]
Query
db.collection.aggregate([{"$match":{"_id":"set1"}},{"$project":{data:{"$arrayToObject":{"$filter":{"input":{"$objectToArray":"$data"},"as":"item","cond":{"$regexMatch":{"input":"$$item.k","regex":"IND.*"}}}}}}}])