Syntax for currying in Scala

val numbers = List.range(1,10); println(numbers.foldLeft(0)(_ +_ ))

or

val numbers = List.range(1,10); println((numbers foldLeft 0)(_ +_ ))

Iterating through command line arguments in Scala

for {
  i <- args.indices.drop(1)
  if args(i) startsWith prefix
} printf("args(%d): %s\n", i, prefix)

or

args.zipWithIndex
    .drop(1)
    .filter {case (s, i) => s startsWith prefix}
    .foreach(arg => println("args("+arg._2+"): "+arg._1))

or

for {
  (s, i) <- args.zipWithIndex.drop(1)
  if s startsWith prefix
} println("args("+i+"): "+s)

Using case classes to filter matching cases in Scala

abstract class A0
 
case class A() extends A0
 
case class B() extends A0
 
case class C() extends A0
 
val list = List( A(), A(), B(), C(), C(), C() )
 
val len1 = list filter ( _  match {case A() => true; case _ => false} ) length

val len2 = list filter ( _  match {case _:A => true; case _ => false} ) length

val len3 = list filter ( x => x match {case A() => true; case _ => false} ) length

printf("=> len1: %d, len2: %d, len3: %d \n",len1,len2,len3)

How to read from a BufferedInputStream in Scala

def bufferedInput(fileName: String) = new BufferedInputStream(new FileInputStream(fileName));  

def bytesAsInts(fileName:String): Iterator[Int] = {
  val in = bufferedInput(fileName)
  Iterator continually in.read() takeWhile (_ != -1)
}

val file = bytesAsInts("test.txt")

file foreach(_=>printf("%c",_:Int))

// AND

file foreach(_=>printf(x=>"%c",x))


//  def isNull[A] = (_: A) == null

How to randomly shuffle a Sequence or List in Scala

val names = List("1","2","3","4","5")

List.fill(names.size)(scala.util.Random.nextInt).zipWithIndex.sortBy(identity).map(_._2).map(names(_))

or

val names = List("1","2","3","4","5","6","7")

Sorting.stableSort(names, (a:String, b:String) => Random.nextInt(2) == 1)
res11: Array[java.lang.String] = Array(2, 7, 4, 5, 1, 6, 3)

How to transform a List into a java.util.List

implicit def toJavaList[A](i: scala.Iterable[A]): java.util.List[A] = {
    val result = new java.util.ArrayList[A]
    i.foreach(result.add)
    java.util.Collections.unmodifiableList[A](result)
  }

Or, if you don't need a immutable List:

implicit def toJavaMutableList[A](i: scala.Iterable[A]): java.util.List[A] = {
    val result = new java.util.ArrayList[A]
    i.foreach(result.add)
    result
}

Example using javaMutableList :

val names = List("1","2","3","4","5","6","7")

val jlist: java.util.List[String] = names
jlist: java.util.List[String] = [1, 2, 3, 4, 5, 6, 7]

val shuffled = java.util.Collections.shuffle(jlist)
shuffled: Unit = ()

println(jlist)
[4, 5, 3, 7, 2, 6, 1]

Arabic-Roman numerals converter written in Scala

A simple arabic to roman numeral converter written in Scala

import scala.collection.SortedMap

def roman(x:Int): String = {

  val romanLiteral = SortedMap(1000 -> "M", 900 -> "CM", 500 -> "D", 400 -> "CD",
    100 -> "C", 90 -> "XC", 50 -> "L", 40 -> "XL", 10 -> "X", 9 -> "IX", 5 ->
    "V", 4 -> "IV", 1 -> "I")

  val arab = romanLiteral.keySet.toList.reverse
  
  def r(n:Int,idx:Int,romanNumber:StringBuilder): String = {

     val a = arab(idx)
  
     if (n==0)
       romanNumber.toString
     else if ( n >= a )
        r( n-a, idx, romanNumber append romanLiteral(a) )
     else
       r( n, idx+1, romanNumber )
  } 

  r(x,0,new StringBuilder())

}

(1 to 100).foreach( x => printf( "%s=%s\n", x, roman(x) ))