[{"id":"1","status":"pending","updated_at":"2018-07-19 13:02:40","created_at":"2018-07-19 12:35:19"},{"id":"2","status":"completed","updated_at":"2018-07-19 13:02:40","created_at":"2018-07-19 12:35:19"},{"id":"3","status":"completed","updated_at":"2018-07-19 13:02:40","created_at":"2018-07-19 12:35:19"},{"id":"4","status":"completed","updated_at":"2018-07-19 13:02:40","created_at":"2018-07-19 12:35:19"},{"id":"5","status":"pending","updated_at":"2018-07-19 13:02:40","created_at":"2018-07-19 12:35:19"},{"id":"5","status":"completed","updated_at":"2018-07-19 13:02:40","created_at":"2018-07-19 12:35:19"},{"id":"5","status":"completed","updated_at":"2018-07-19 13:02:40","created_at":"2018-07-19 12:35:19"}]

db.collection.aggregate([{$group:{_id:"$id",pending:{$sum:{$cond:[{"$eq":["$status","pending"]},1,0]}},completed:{$sum:{$cond:[{"$eq":["$status","completed"]},1,0]}}}}])