Scala列表数组学习

数组

不可变数组——定义、查询、增加、循环

//定义数据
    var arr: Array[Int] = new Array[Int](5)
    
    var arr2 = Array(2, 3, 42, 21, 3)
    //循环以及查询数据
    for (i <- 0 until arr2.length) {
      println(arr2(i))
    }
    for (i <- arr2.indices) {
      println(arr2(i))
    }
    for (elem <- arr2) {
      println(elem)
    }
    var iter = arr2.iterator
    while (iter.hasNext)
      println(iter.next())
    arr2.foreach(println)
  
    //增加数据
    var newArr = arr2.:+(73)
    println(newArr)

可变数组——定义，增加（循环与查询与不可变的一样）

    //可变数组
    var arr3: ArrayBuffer[Int] = new ArrayBuffer[Int]()
    var arr4 = ArrayBuffer(23, 21, 32)

    arr3.append(32)
    arr3.insert(0, 4)
    arr4.append(5)
    println(arr3) // (4, 32)
    println(arr4) // (23, 21, 32, 5)

列表操作

    // 创建不可变列表
    var list1 = List(1, 2, 3)
    list1.foreach(println)
    var list5 = 32 :: 14 :: Nil
    var list6 = 21 :: 1 :: Nil
    var list7 = list5 ::: list6
    println(list7)

    // 创建可变列表
    val list8 : ListBuffer[Int] = new ListBuffer[Int]()
    list8.append(15, 23)
    val list9 = ListBuffer(12, 52, 21)
    var list3 = list8 ++ list9

Set操作

    // 不可变set
    val set1 = Set(3, 21, 4)
    println(set1)

    val set2 = set1 + 20
    val set3 = set1 ++ set2
    println(set3)

    // 可变set
    val set4: mutable.Set[Int] = mutable.Set(12, 32, 33, 23, 43)
    set4.add(4)
    set4.remove(12)
    println(set4)

Map操作

    // 可变map
    val map2 : mutable.Map[String, Int] = mutable.Map("a"-> 13, "b" -> 32)
    map2.put("c", 23)
    map2.remove("a")
    map2.update("b", 2)
    for (key <- map2.keys) {
      println(s"${key} --->${map1.get(key)}" )
    }
    // 如果没有对应键
    println(map2.getOrElse("c", 0))

集合并集、交集、差集

    val list10 = List(1, 2, 3, 5, 8)
    val list11 = List(2, 3, 9, 10, 22)

    // 并集, 如果基础集合为Set，会自动去重
    val union = list10.union(list11)
    println(union)

    // 交集
    val intersection = list10.intersect(list11)
    println(intersection)

    // 差集
    val diff1 = list10.diff(list11)
    val diff2 = list11.diff(list10)

    println(diff1, diff2)

集合计算（求和、求乘积、最大值、最小值、排序）

    val list12 = List(2, 3, 9, 10, 22)

    // 求和
    println(list12.sum)

    // 求乘积
    println(list12.product)

    // 最大值、最小值
    println(list12.max)
    println(list12.min)

    // 排序
    var sortedList = list12.sorted
    // 正序
    println(sortedList)
    // 倒序
    println(sortedList.reverse)

    // 从小到大排序，以下等同
    println(list12.sortWith((a: Int, b: Int) => {a < b}))
    println(list12.sortWith(_ < _))

集合扁平化、分组计算、聚合、fold、merge合并、wordCount计算

    var list15 = List(1, 2, 3, 4, 5, 6, 7, 8, 9)

    // 把集合中每个数乘2
    println(list15.map(_ * 2))

    // 扁平化
    val nestedList: List[List[Int]] = List(List(1, 2, 3), List(4, 5), List(6,7,8,9))
    val flatList = nestedList.flatten
    println(flatList)

    // 分组
    val groupMap : Map[Int, List[Int]] = list15.groupBy(_ % 2)
    println(groupMap)

    // 聚合
    val reduceList = list15.reduce(_ - _) // 1-2-3-4-5-6-7-8-9
    println(reduceList)

    // fold
    println(list15.fold(20)(_ + _)) // 20 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9

    // merge合并
    val map3 = Map("a" -> 1, "b" -> 3, "c" -> 5)
    val map4 = mutable.Map("a" -> 2, "b" -> 2, "c" -> 4)

    val map5 = map3.foldLeft(map4)(
      (mergedMap, kv) => {
        val key = kv._1
        val value = kv._2
        mergedMap(key) = mergedMap.getOrElse(key, 0) + value
        mergedMap
      }
    )
    println(map5)

    val StringList : List[String] = List(
      "hello",
      "hello spark ",
      "hello world",
      "hello scala",
      "hello spark from",
      "hello scala hehe"
    )

    val wordList = StringList.flatMap(_.split(" "))
    println(wordList)

    val groupMap1: Map[String, List[String]] = wordList.groupBy(word => word)

    val stringToInt: Map[String, Int] = groupMap1.map(kv => (kv._1, kv._2.length))

    val sortList2: List[(String, Int)] = stringToInt.toList.sortWith(_._2 > _._2)
    println(sortList2)