com.yahoo.sketches.hive.tuple.DoubleSummarySketchToPercentileUDF 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 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.quantiles.DoublesSketch;
import com.yahoo.sketches.quantiles.UpdateDoublesSketch;
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 = "DoubleSummarySketchToPercentile",
value = "_FUNC_(sketch)",
extended = "Returns a percentile from a given Sketch."
+ " The values from DoubleSummary objects in the sketch are extracted, and"
+ " a single value with a given normalized rank is returned. The rank is in"
+ " percent. For example, 50th percentile is the median value of the"
+ " distribution (the number separating the higher half of a probability"
+ " distribution from the lower half)")
public class DoubleSummarySketchToPercentileUDF extends UDF {
private static final int QUANTILES_SKETCH_SIZE = 1024;
/**
* Get percentile from a given Sketch<DoubleSummary>
* @param serializedSketch DoubleSummarySketch in as serialized binary
* @param percentile normalized rank in percent
* @return percentile value
*/
public Double evaluate(final BytesWritable serializedSketch, final double percentile) {
if (serializedSketch == null) { return null; }
if ((percentile < 0) || (percentile > 100)) {
throw new IllegalArgumentException("percentile must be between 0 and 100");
}
final Sketch sketch =
Sketches.heapifySketch(Memory.wrap(serializedSketch.getBytes()));
final UpdateDoublesSketch qs = DoublesSketch.builder().setK(QUANTILES_SKETCH_SIZE).build();
final SketchIterator it = sketch.iterator();
while (it.next()) {
qs.update(it.getSummary().getValue());
}
return qs.getQuantile(percentile / 100);
}
}