Revised Scala version from this blog post: http://blogs.sourceallies.com/2009/12/word-counts-example-in-ruby-and-scala

wordcounts.scala

import java.io._
val rootDir = new File("/home/zcox/dev/20_newsgroups")
if (!rootDir.exists) throw new IllegalArgumentException(rootDir + " does not exist")

var counts = Map.empty[String, Int].withDefaultValue(0)
files(rootDir) { _.split("""\W+""").foreach { word => counts = counts(word.toLowerCase) += 1 }}
write(counts, "counts-descreasing-scala") {_._2 > _._2}
write(counts, "counts-alphabetical-scala") {_._1 < _._1}
 
/** Writes the specified map to the specified file in tab-delimited format, sorted accordingly. */
def write[K, V](map: Map[K, V], file: String)(sort: (Tuple2[K, V], Tuple2[K, V]) => Boolean) {
  using (new PrintWriter(new FileWriter(file))) { out => 
    map.toList.sort(sort).foreach { pair => out.println(pair._1 + "\t" + pair._2) }
  }
}

/** Iterates over all files under rootDir, opens each one and passes it to the function */
def files(rootDir: File)(process: File => Unit) {
  for (dir <- rootDir.listFiles; if dir.isDirectory) {
    for (file <- dir.listFiles; if file.isFile) {
      process(file)
    }
  }
}
 
/** Converts a File to a String. */
implicit def file2String(file: File): String = scala.io.Source.fromFile(file, "ISO-8859-1").mkString
 
/** Performs some operation on the specified closeable object and then ensures it gets closed. */
def using[Closeable <: {def close(): Unit}, B](closeable: Closeable)(getB: Closeable => B): B = 
  try {
    getB(closeable)
  } finally {
    closeable.close()
  }