sortBy(-_._2 ) in scala

_._2表示按照第二个字符进行排序
前面的-号表示逆序（降序）排序，默认是升序排序

scala> List(1,2,3).sortBy(-_)
res0: List[Int] = List(3, 2, 1)scala> List("a"->1,"b"->2, "c"->3).sortBy(-_._2)
res1: List[(String, Int)] = List((c,3), (b,2), (a,1))scala> List(1,2,3).sortBy(x => -x)
res2: List[Int] = List(3, 2, 1)

转载自：
https://stackoverflow.com/questions/35814836/understanding-scala-code-2

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