docs: protected double estimateID(DBIDRef ignore, DoubleDBIDListIter it, double[] p) {
      int j = 0;
      for(it.seek(0); it.valid(); it.advance()) {
        if(it.doubleValue() == 0. || DBIDUtil.equal(ignore, it)) {
          continue;
        }
        p[j++] = it.doubleValue();
      }
      if(j < 2) {
        throw new ArithmeticException("Too little data to estimate ID.");
      }
      return estimator.estimate(p, j);
    }