public void dropDataSegment(final int iId) {
   if (iId < dataSegments.size()) {
     dataSegments.set(iId, null);
     update();
   }
 }
 public void dropCluster(final int iClusterId) {
   if (iClusterId < clusters.size()) {
     clusters.set(iClusterId, null);
     update();
   }
 }