com.yahoo.sketches.hive.tuple.DoubleSummarySketchToEstimatesUDF Maven / Gradle / Ivy
/*
* Copyright 2016, Yahoo! Inc.
* Licensed under the terms of the Apache License 2.0. See LICENSE file at the project root for terms.
*/
package com.yahoo.sketches.hive.tuple;
import java.util.Arrays;
import java.util.List;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.BytesWritable;
import com.yahoo.memory.Memory;
import com.yahoo.sketches.tuple.DoubleSummary;
import com.yahoo.sketches.tuple.Sketch;
import com.yahoo.sketches.tuple.SketchIterator;
import com.yahoo.sketches.tuple.Sketches;
@Description(
name = "DoubleSummarySketchToEstimates",
value = "_FUNC_(sketch)",
extended = "Returns a list of estimates from a given Sketch."
+ " The result will be two double values."
+ " The first estimate is the estimate of the number of unique keys in the"
+ " original population. Next there is an estimate of the sum of the parameter in the"
+ " original population (sum of the values in the sketch scaled to the original population."
+ " This estimate assumes that the DoubleSummary was used in the Sum mode.)")
public class DoubleSummarySketchToEstimatesUDF extends UDF {
/**
* Get estimates from a given Sketch<DoubleSummary>
* @param serializedSketch DoubleSummarySketch in a serialized binary form
* @return list of estimates
*/
public List evaluate(final BytesWritable serializedSketch) {
if (serializedSketch == null) { return null; }
final Sketch sketch =
Sketches.heapifySketch(Memory.wrap(serializedSketch.getBytes()));
double sum = 0;
final SketchIterator it = sketch.iterator();
while (it.next()) {
sum += it.getSummary().getValue();
}
return Arrays.asList(
sketch.getEstimate(),
sum / sketch.getTheta()
);
}
}