private void registerFrequencies() {
    SketchDescriptor sd = new SketchDescriptor("freq");

    sd.register(DATA_TO_SKETCH, org.apache.datasketches.hive.frequencies.DataToStringsSketchUDAF.class);
    // FIXME: missing?
    //registerUDF(org.apache.datasketches.hive.frequencies.DoublesSketchToStringUDF.class, p + SKETCH_TO_STRING);
    //registerUDF(org.apache.datasketches.hive.quantiles.UnionItemsSketchUDAF.class, p + UNION_SKETCH);
    sd.register(UNION_SKETCH, org.apache.datasketches.hive.frequencies.UnionStringsSketchUDAF.class);
    sd.register(GET_FREQUENT_ITEMS,
        org.apache.datasketches.hive.frequencies.GetFrequentItemsFromStringsSketchUDTF.class);
    sketchClasses.put("freq", sd);
  }
Registers functions from the DataSketches library as builtin functions.

In an effort to show a more consistent
ql/src/java/org/apache/hadoop/hive/ql/exec/DataSketchesFunctions.java