[{"category":"Privacy","response":1},{"category":"Mobile","response":1},{"category":"Privacy","response":1},{"category":"Privacy","response":2}]

db.collection.aggregate([{$facet:{data:[{$match:{}}],total:[{$group:{_id:"",Total:{$sum:"$response"}}}]}},{$unwind:"$data"},{$unwind:"$total"},{$replaceRoot:{newRoot:{$mergeObjects:["$total","$data"]}}}])