[{_id:ObjectId("6179a02db235317ce6511429"),song:"BIBLICAL",artist:"CALUM SCOTT",expProg:"Autoplay",actProg:"Autoplay",playedAt:1635360813},{_id:ObjectId("6179a117b235317ce651142a"),song:"WILL YOU STILL LOVE ME?",artist:"CHICAGO",expProg:"Autoplay",actProg:"Autoplay",playedAt:1635361047},{_id:ObjectId("6179a20cb235317ce651142b"),song:"SHY GUY",artist:"DIANA KING",expProg:"Autoplay",actProg:"Autoplay",playedAt:1635361292}]

db.collection.aggregate([{"$group":{"_id":"$song","count":{"$sum":1}}},{"$replaceRoot":{"newRoot":{"$arrayToObject":[[{"k":"$_id","v":"$count"}]]}}}])