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db.collection.aggregate([{$group:{_id:{id:"$id",type:{$arrayElemAt:[{$split:[{$toLower:"$info.batch"},"-"]},1]}},docs:{$push:"$batchElements.elements"}}},{$group:{_id:"$_id.id",data:{$push:{k:{$concat:["$_id.type","Elements"]},v:"$docs"}}}},{$replaceRoot:{newRoot:{$mergeObjects:[{_id:"$_id"},{$arrayToObject:"$data"}]}}}])