groupBy example.scala

  /** Converts the word into its character occurrence list.
   *
   *  Note: the uppercase and lowercase version of the character are treated as the
   *  same character, and are represented as a lowercase character in the occurrence list.
   *
   *  Note: you must use `groupBy` to implement this method!
   */
  def wordOccurrences(w: Word): Occurrences = w.toLowerCase.groupBy(char => char).map{
    case (char, repetitions) => (char, repetitions.length)
  }.toList.sortBy{ case (char, _) => char}