sortBy（）
定义：
def sortBy[B](fun: (A) =>B)
栗子1:
val words = "the quick brown fox jumped over the lazy dog"
val words_split = words.split(" ")
words_split.sortBy(x =>(x.length, x.head) ) // 按照右边的（x.length, x.head）进行排序
output: The, dog, fox, the, lazy, over, brown, quick, jumped
栗子2:
val myseq1 = Array((3,1,2,5),(2,4,5,1),(8, 2, 4,9)
myseq1.sortBy(_._1).foreach(println)