Scala reverse string

Note that there is already defined function:

scala> val x = "scala is awesome"
x: java.lang.String = scala is awesome

scala> x.reverse
res1: String = emosewa si alacs

But if you want to do that by yourself:

def reverse(s: String) : String =
(for(i <- s.length - 1 to 0 by -1) yield s(i)).mkString

or (sometimes it is better to use until, but probably not in that case)

def reverse(s: String) : String =
(for(i <- s.length until 0 by -1) yield s(i-1)).mkString

Also, note that if you use reversed counting (from bigger one to less one value) you should specify negative step or you will get an empty set:

scala> for(i <- x.length until 0) yield i
res2: scala.collection.immutable.IndexedSeq[Int] = Vector()

scala> for(i <- x.length until 0 by -1) yield i
res3: scala.collection.immutable.IndexedSeq[Int] = Vector(16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

You could also write this using a recursive approach (throwing this one in just for fun)

def reverse(s: String): String = {
  if (s.isEmpty) ""
  else reverse(s.tail) + s.head
}

Here's a short version

def reverse(s: String) = ("" /: s)((a, x) => x + a)

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edit : or even shorter, we have the fantastically cryptic

def reverse(s: String) = ("" /: s)(_.+:(_))

but I wouldn't really recommend this...