[{"_id":ObjectId("5e551b2e63a0f1fc55f026dd"),"dateHour":"2020-02-25 13","detail":[{"campaignId":"5e4a937b459418737cc1dfa5","timestamp":"2020-02-25 13:03:626","msisdn":"050920305373677038659253736080036024-1582133696781",},{"campaignId":"5e4a937b459418737cc1dfa5","timestamp":"2020-02-26 13:04:626","msisdn":"050920305373677038659253736080036024-1582133696781",},{"campaignId":"5e4a937b459418737cc1dfa5","timestamp":"2020-02-25 13:06:626","msisdn":"050920305373677038659253-1582133696781",},{"campaignId":"5e4a937b459418737cc1dfa5","timestamp":"2020-02-25 13:06:626","msisdn":"050920305373677038659253-1582133696781345688",}]}]

db.collection.aggregate([{$unwind:"$detail"},{$addFields:{"dHr":{$substr:["$dateHour",0,10]}}},{$group:{_id:"$dHr",msisdn:{$addToSet:"$detail.msisdn"}}},{$project:{_id:0,date:"$_id",count:{$size:"$msisdn"}}}])