public static DBIDs randomSample(DBIDs ids,double rate,RandomFactory random){
  return randomSample(ids,rate,random.getSingleThreadedRandom());
}

public static DBIDs randomSample ( DBIDs ids , double rate , RandomFactory random ) { return randomSample ( ids , rate , random . getSingleThreadedRandom ( ) ) ; }
produce a random sample of the given dbids .
