Для Swift 4 для меня работало следующее:
let dicNumArray = ["q":[1,2,3,4,5],"a":[2,3,4,5,5],"s":[123,123,132,43,4],"t":[00,88,66,542,321]] let sortedDic = dicNumArray.sorted { (aDic, bDic) -> Bool in return aDic.key < bDic.key }