*     Arrays.asList("Inky", "Blinky", "Pinky", "Pinky", "Clyde");
   * Function<String, Integer> stringLengthFunction = ...;
   * Multimap<Integer, String> index =
   *     Multimaps.index(badGuys, stringLengthFunction);
   * System.out.println(index);
   * }</pre>
   *
   * <p>prints
   *
   * <pre>{@code
   * {4=[Inky], 6=[Blinky], 5=[Pinky, Pinky, Clyde]}
   * }</pre>
   *