public static ModifiableDBIDs union(DBIDs ids1,DBIDs ids2){
  ModifiableDBIDs result=DBIDUtil.newHashSet(Math.max(ids1.size(),ids2.size()));
  result.addDBIDs(ids1);
  result.addDBIDs(ids2);
  return result;
}

public static ModifiableDBIDs union ( DBIDs ids1 , DBIDs ids2 ) { ModifiableDBIDs result = DBIDUtil . newHashSet ( Math . max ( ids1 . size ( ) , ids2 . size ( ) ) ) ; result . addDBIDs ( ids1 ) ; result . addDBIDs ( ids2 ) ; return result ; }
returns the union of the two specified collection of ids .
