IPSWAYS Scala Meetup - Collections

Collections.scala

  // List (immutable)
  val numbers: List[Int] = List(1, 2, 6, 34, 17, 42, 54, 100, 117, 1337)
  
  // Map (immutable)
  val map = Map("Test" -> 4, "ABC" -> 4)

  // List API
  // Filter
  numbers.filter(x => x < 4)
  numbers.filter(_ < 4)

  // Map
  numbers.map(x => x * x)
  // foreach, Seiteneffekt (Unit)
  numbers.foreach(x => println(x * x))

  numbers.exists(_ == 42)
  numbers.exists(_ == 0)

  numbers.partition(_ > 100)
  numbers.take(2)

  numbers.takeWhile(_ < 100)
  numbers.count(_ < 100)

  numbers.mkString(", ")

  numbers.reverse

  val consList = "Test" :: "ABC" :: Nil

  // Zip
  val chars = List("a", "b", "c")

  numbers.zip(chars)

  // Fold -> Addieren einzelner Ergebnisse
  case class Score(p1: Int, p2: Int)

  val scores = Seq(Score(5, 1), Score(2, 5), Score(1, 5))

  // The java way
  var totalScoreP1: Int = 0
  var totalScoreP2: Int = 0
  for (score <- scores) {
    totalScoreP1 += score.p1
    totalScoreP2 += score.p2
  }

  s"Total score: ${totalScoreP1} : ${totalScoreP2}"

  //  List[Score] => (p1ScoreTotal: Int, p2ScoreTotal: Int)

  val initialTotal = (0, 0)
	
	// 1. (0, 0), Score(5, 1) => (5, 1)
	// 2. (5, 1), Score(2, 5) => (5 + 2, 1 + 5)
	// 3. (7, 6), Score(1, 5) => (7 + 1, 6 + 5)
	// Result: (8, 11)
	
  val totalScores = scores.foldLeft(initialTotal) ((total, current) => (total._1 + current.p1, total._2 + current.p2))

  s"Total score: ${totalScores._1} : ${totalScores._2}"
  
  // Parallel collections
  numbers.par.filter(_ > 100)