[{"auditMessages":{eventMetaData:[{"Counterparty Name":"Mr Jalel CHAHED",abc:1,"Transaction Amount":"4.32"},{"Counterparty Name":"Mr Jalel CHAHED",abc:11,"Transaction Amount":"4.32"},{"Counterparty Name":"Mr Jalel CHAHED",abc:12,"Transaction Amount":"1.32"},{"Counterparty Name":"Mr Jalel CHAHED",abc:122,"Transaction Amount":"1.32"}]}},{"auditMessages":{eventMetaData:[{"Counterparty Name":"Mr Jalel CHAHED2",abc:11,"Transaction Amount":"5.32"},{"Counterparty Name":"Mr Jalel CHAHED2",abc:1,"Transaction Amount":"5.32"},{"Counterparty Name":"Mr Jalel CHAHED2",abc:122,"Transaction Amount":"2.32"},{"Counterparty Name":"Mr Jalel CHAHED2",abc:1222,"Transaction Amount":"2.32"}]}}]

db.collection.aggregate([{$project:{account:{$arrayElemAt:["$auditMessages.eventMetaData.Counterparty Name",0]},total:{$reduce:{input:"$auditMessages.eventMetaData.Transaction Amount",initialValue:0,in:{$trunc:[{$add:["$$value",{$toDouble:"$$this"}]},2]}}}}}])