@Override
  public void transform(Row row, PointCollector collector) throws Exception {
    if (row.isNull(0)) {
      valueArrayList.add(Double.NaN);
    } else {
      valueArrayList.add(Util.getValueAsDouble(row, 0));
    }
  }
This function calculates auto-correlation factor of a single input series.
library-udf/src/main/java/org/apache/iotdb/library/dprofile/UDTFACF.java