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db.collection.aggregate([{$addFields:{locations:{$map:{input:"$locations",as:"l",in:{$mergeObjects:["$$l",{category:{$reduce:{input:{$objectToArray:"$$l"},initialValue:null,in:{$cond:[{$eq:["$$this.k","$sort_category"]},"$$this.v","$$value"]}}}}]}}}}},{$unwind:"$locations"},{$sort:{"locations.category":1}},{$project:{"locations.category":0}},{$group:{_id:"$_id",customer:{$first:"$customer"},sort_category:{$first:"$sort_category"},locations:{$push:"$locations"}}},{$project:{_id:0}}])