[{"_id":"2DLQFJLbZScBXpSam","toilet_id":"bJsyfh3TCvpTzE2mJ","reason_ids":["KNcKQCjhFzha3oLfE","KW7Kcsv7835YZeE3n"],"score_id":null,"toilet":{"_id":"bJsyfh3TCvpTzE2mJ","name":"Toilet_M_1","gender":"m","mac_address":"11:11:11:11:11:11"}},{"_id":"akjsbcjascklsacas","toilet_id":"bJsyfh3TCvpTzE2mJ","reason_ids":["KW7Kcsv7835YZeE3n"],"score_id":null,"toilet":{"_id":"fsgndgklndsdsdsd","name":"Toilet_F_1","gender":"f","mac_address":"11:11:11:11:11:11"}},]

db.collection.aggregate([{"$unwind":"$reason_ids"},{"$group":{"_id":"$reason_ids","count":{"$sum":1}}}])