code: public static Map groupBy(Object[] self, Object... closures) {
          return groupBy((Iterable)Arrays.asList(self), closures);
      }
docs: Sorts all array members into (sub)groups determined by the supplied
  mapping closures as per the Iterable variant of this method.
  
  @param self     an array to group
  @param closures an array of closures, each mapping entries on keys
  @return a new Map grouped by keys on each criterion
  @see #groupBy(Iterable, Object...)
  @see Closure#IDENTITY
  @since 2.2.0