for(Iterator<DBID> clusterIter = list.iterator(); clusterIter.hasNext();) {
if(mean == null) {
mean = database.get(clusterIter.next()).getColumnVector();
}
else {
mean.plusEquals(database.get(clusterIter.next()).getColumnVector());
}
}
if(list.size() > 0) {
assert mean != null;
mean.timesEquals(1.0 / list.size());