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def main(args: Array[String]){
(1 to 9).map("*" * _).foreach(println _)
(1 to 9).filter(_ % 2 == 0) .foreach(println)
println((1 to 9).reduceLeft(_ * _))
"Spark is the most exciting thing happening in big data today".split(" ").
sortWith(_.length < _.length).foreach(println)
val fun = ceil _
val num = 3.14
println(fun(num) )
Array(3.14, 1.42, 2.0).map(fun).foreach(println)
val triple = (x: Double) => 3 * x
Array(3.14, 1.42, 2.0).map((x: Double) => 3 * x)
Array(3.14, 1.42, 2.0).map{ (x: Double) => 3 * x }
def high_order_functions(f: (Double) => Double) = f(0.25) //定义函数high_order_functions，参数是另一个函数f，f的参数是Double，返回值也是Double，具体表现形式是f(0.25)
println(high_order_functions(ceil _)) //具体为ceil(0.25)
println(high_order_functions(sqrt _)) //具体为sqrt(0.25)
def mulBy(factor: Double) = (x: Double) => factor * x //定义函数mulBy，参数是x
val quintuple = mulBy(5)
println(quintuple(20))
println(high_order_functions((x: Double) => 3 * x))
high_order_functions((x) => 3 * x)
high_order_functions(x => 3 * x)
println(high_order_functions(3 * _))
val fun2 = 3 * (_: Double)
val fun3: (Double) => Double = 3 * _
}

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Scala的高阶函数