mapOpDemo_2.scala

package ScalaBasic

object mapOpDemo_2 extends App {

  // example 1 : add one to element
  val list1 = List(1,2,3,4,5,6,7,8)
  val r1 = list1.map( x => {
    val tmp = x
    println ("tmp = " + tmp)
    x + 1
  })

  r1.foreach(println(_))

  println("====================")

  // example 2 : filter even
  val r2 = list1.filter(x => {x % 2 == 0})

  r2.foreach(println(_))

  println("====================")

  // example 3 : flatMap
  val l2 = List("a", "b", "c")
  val r3 = l2.flatMap(_ + "|")
  println("r3 = " + r3)

  println("====================")

  // example 4 : Map & reduce
  // https://www.geeksforgeeks.org/scala-reduce-function/
  val l4 = List("a", "b", "c", "d", "a", "b")
  val r4 = l4.map( x => {
    val tmp = (x,1)
    tmp
  }).groupBy(_._1)
    //.reduce((x,y) => {x._1 + y._2})
    //.flatMap(x => {x._1})
    .toList


  println("r4 = " + r4)

  println("====================")

  // example 5 : map with case class
  case class User(
                   id: String,
                   age: Int
                 )

  val user1 = User("001", 20)
  val user2 = User("002", 70)
  val user3 = User("003", 10)

  val users = List(user1, user2, user3)

  // V1 : map + pattern match
  val users_filter = users.map(x => x match {
    case _ if x.age > 10 => x
    case _ =>
  })

  // V2 : partial function
  users_filter.filter(x => x != "").foreach(println(_))

  println("====================")

  val users_filter2 = users.collect{case x:User if x.age > 10 => x}
  users_filter2.foreach(println(_))


  println("====================")

  // example 6 : map with complex case class
  case class Record(
    id: String,
    msg: Array[String]
  )

  val record1 = Record("001", Array("aaa", "bbb", "ccc"))
  val record2 = Record("002", Array("hello", "world", "!!!"))
  val record3 = Record("003", Array("aaa", "kkk", "aaa", "zzz"))

  val records = List(record1, record2, record3)

  val records_filter = records.collect{
    case x:Record  if x.msg(0) == "aaa" => (x.id, x.msg.toList)
  }

  records_filter.foreach(println(_))
}