public void testUDAF() {

    DataFrame df = hc.range(0, 100).unionAll(hc.range(0, 100)).select(col("id").as("value"));

    UserDefinedAggregateFunction udaf = new MyDoubleSum();

    UserDefinedAggregateFunction registeredUDAF = hc.udf().register("mydoublesum", udaf);

    DataFrame aggregatedDF =

      df.groupBy()

        .agg(

          udaf.distinct(col("value")),

          udaf.apply(col("value")),

          registeredUDAF.apply(col("value")),

          callUDF("mydoublesum", col("value")));



    List<Row> expectedResult = new ArrayList<>();

    expectedResult.add(RowFactory.create(4950.0, 9900.0, 9900.0, 9900.0));

    checkAnswer(

      aggregatedDF,

      expectedResult);

  }