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db.collection.aggregate([{$project:{_id:1,firstName:1,lastName:1,maritalStatus:1,createdBy:1,createdAt:1,__v:1,lastTreatment:{$max:"$treatments.treatmentDate"},diagnoses:{$reduce:{input:"$treatments",initialValue:[],in:{$setUnion:["$$value","$$this.diagnoses"]}}}}}])