groupBy
val array: Array[Int] = Array(1,2,3,4,5)
val list = List(1,2,3,4)
val map = Map(("a",1),("b",2),("c",3))
val set = Set(1,3,4,5)
val tuple: (Int, Int, Int, Int) = (1,2,3,4)
//Map(分组key -> List(元素))
println(list.groupBy(num => num))
println(list.groupBy(num => num%2))
val strings = List("Hello", "Hive", "Hbase","Spark","Scala")
println(strings.groupBy(_.substring(0, 1)))
Map(2 -> List(2), 4 -> List(4), 1 -> List(1), 3 -> List(3))
Map(1 -> List(1, 3), 0 -> List(2, 4))
Map(S -> List(Spark, Scala), H -> List(Hello, Hive, Hbase))
