code: public static int median(ArrayModifiableDBIDs data, Comparator<? super DBIDRef> comparator) {
      return median(data, comparator, 0, data.size());
    }
docs: Compute the median of an array efficiently using the QuickSelect method.
  
  Note: the array is <b>modified</b> by this.
  
  @param data Data to process
  @param comparator Comparator to use
  @return Median position