Database
[{"_id":"5facde3f9dXXXXXXX208","LoaDiagnosis":[{"IcdCode":"S06.0","CronicIllness":{"ChronicIllnessTagging":"N"}},{"IcdCode":"S06.0","CronicIllness":{"ChronicIllnessTagging":"N"}}]}]
Query
db.collection.aggregate([{$unwind:"$LoaDiagnosis"},{$group:{_id:"$_id",icds_chronic:{$addToSet:{$cond:{if:{$eq:["$LoaDiagnosis.CronicIllness.ChronicIllnessTagging","N"]},then:"$LoaDiagnosis.IcdCode",else:"$$REMOVE"}}},}}])