Spark学习使用笔记 - Scala篇（2）- 数组

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数组：

定长数组：

val s = Array("Hello", 1)//用()而不是[]println("s(0) -> " + s(0)) //输出s(0) -> Hello

变长数组：

val b = ArrayBuffer[Int]()// += 末尾增加元素或者元祖b += 1b +=(2, 3)println(b) //输出ArrayBuffer(1, 2, 3)// ++= 末未添加人以及和b ++= Array(4, 5, 6)println(b) //输出ArrayBuffer(1, 2, 3, 4, 5, 6)//trimEnd，去掉末尾的n个元素b.trimEnd(1)println(b) //输出ArrayBuffer(1, 2, 3, 4, 5)//末尾添加最高效，插入和移除涉及到平移，效率会差一些b.insert(2, 22)//插入多个b.insert(2, 222, 2222, 22222)println(b) //输出ArrayBuffer(1, 2, 222, 2222, 22222, 22, 3, 4, 5)//移除第二个元素b.remove(2)println(b) //输出ArrayBuffer(1, 2, 2222, 22222, 22, 3, 4, 5)//移除从第二个开始，3个元素b.remove(2, 3)println(b) //输出ArrayBuffer(1, 2, 3, 4, 5)println(b.toArray) //输出[I@755d828fprintln(b.toArray.toBuffer) //输出ArrayBuffer(1, 2, 3, 4, 5)

遍历数组

println("----------------跨2步长---------------------")for (i <- 0 until(10, 2))  print(i) //输出02468println("\n----------------逆转----------------------")for (i <- (0 until(10, 2)).reverse)  print(i) //输出86420println("\n----------------遍历数组--------------------")val a = Array(1, 2, 3, "abc")for (i <- a)  print(i) //输出123abcprintln("\n------------------------------------------")

数组变换：

    val arr1 = Array(1, 2, 3, 4, 5, 6)    val result1 = for (i <- arr1) yield i * 10    println(result1) //输出[I@39b0595c    val arr2 = ArrayBuffer[Int]()    arr2 +=(1, 2, 3, 4, 5, 6)    val result2 = for (i <- arr2) yield i    println(result2) //输出ArrayBuffer(1, 2, 3, 4, 5, 6)    println("------------------------------------------")    val result3 = for (i <- arr2 if i % 2 == 0) yield i * 10    val result4 = arr2.filter(_ % 2 == 0).map(_ * 10)    println(result3) //输出ArrayBuffer(20, 40, 60)    println(result4) //输出ArrayBuffer(20, 40, 60)    //去掉第一个负数以外的负数    val a = ArrayBuffer(1, 2, 3, 4, -5, 8, -1, 7, -2)    var first = true    val result5 = for (i <- a if i > 0 || first) yield {      if (i < 0)        first = false      i    }    println(result5) //输出ArrayBuffer(1, 2, 3, 4, -5, 8, 7)

常用函数

    println(Array(1, 2, 10).sum) //输出：13    //数组类型不能是any，否则无法比较    println(Array("Mary", "had", "a", "little", "lamp").max) //输出：little    val a = ArrayBuffer(324, 123.2, 123, 23, 4, 12, 7)    println(a.sorted.reverse) //输出：ArrayBuffer(324.0, 123.2, 123.0, 23.0, 12.0, 7.0, 4.0)    val b = a.toArray    scala.util.Sorting.quickSort(b)    println(b.mkString("<", ",", ">")) //输出：<4.0,7.0,12.0,23.0,123.0,123.2,324.0>

其他：

    val a = ArrayBuffer[Int](1, 2, 3)    a.append(4, 5, 6)    println(a.mkString("<", ",", ">")) //输出<1,2,3,4,5,6>    println(a.count(_ > 2)) //输出：4    //以上代码相当于：    def f(x: Int) = {      if (x > 2)        true      else        false    }    println(a.count(f)) //输出：4    //+= -= 返回this，所以我们可以用链式    a +=(1, 2, 3) -= 1 -= 5 //-= 去掉第一个为1和为5的元素    println(a) //输出：ArrayBuffer(2, 3, 4, 6, 1, 2, 3)

多维数组：

    val matrix1 = Array.ofDim[Int](3, 4) //二维数组    val matrix2 = Array.ofDim[Int](3, 4, 5) //三维数组    matrix1(1)(2) = 1    matrix2(1)(2)(3) = 1    println(matrix1.mkString("<", ",", ">")) //输出：（数组地址）<[I@a54a40c,[I@3ade1520,[I@4a3d0611>    println(matrix2.mkString("<", ",", ">")) //输出：<[[I@6c596c2a,[[I@62cc70f8,[[I@5c0cdc74>    val triangle = new Array[Array[Int]](10)    for (i <- 0 until triangle.length) {      triangle(i) = new Array[Int](i)    }

练习：

def ex1(n: Int) = {    val a = new Array[Int](n)    for (i <- 0 until a.length) {      a(i) = Random.nextInt(n)    }  }  def swapAdjoin(n: Array[Int]): Array[Int] = {    var count = -1    for (i <- n) yield {      count += 1      if (count % 2 == 0) {        if (count + 1 < n.length)          n(count + 1)        else          i      } else {        n(count - 1)      }    }  }  def ex2_3 = {    println(swapAdjoin(Array(1, 2, 3, 4, 5)).mkString("<", ",", ">")) //输出：<2,1,4,3,5>  }  def classify(n: Array[Int]): Array[Int] = {    val a = (for (i <- n if i > 0) yield i).toBuffer    a.appendAll(for (i <- n if i <= 0) yield i)    a.toArray  }  def ex4 = {    println(classify(Array(1, 2, 3, 0, -1, 2, 3, 45, -32, -43, 2, 0)).mkString("<", ",", ">"))//输出：<1,2,3,2,3,45,2,0,-1,-32,-43,0>  }  def arrayAverage(n:Array[Double]):Double = {    n.sum/n.length  }  def ex5 = {     println(arrayAverage(Array(1,2,3,5.0,7.9))) //输出3.78  }  def ex7 = {    println(Array(1,2,3,4,5,1,12,2,3,4,5,2,3,4,6,8).distinct.mkString("<", ",", ">"))//输出：<1,2,3,4,5,12,6,8>  }

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