@Override
  public void transform(Row row, PointCollector collector) throws Exception {
    double v = Util.getValueAsDouble(row);
    if (Double.isFinite(v)) {
      list.add(v);
    }
  }
This function does Fast Fourier Transform for input series.
library-udf/src/main/java/org/apache/iotdb/library/frequency/UDTFFFT.java