com.yahoo.sketches.hive.theta.EstimateSketchUDF 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.theta;
import static com.yahoo.sketches.Util.DEFAULT_UPDATE_SEED;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.BytesWritable;
import com.yahoo.memory.Memory;
import com.yahoo.sketches.theta.Sketch;
/**
* Hive estimate sketch udf. V4
*
*/
public class EstimateSketchUDF extends UDF {
private static final int EMPTY_SKETCH_SIZE_BYTES = 8;
/**
* Returns the estimate unique count of sketch.
*
* @param binarySketch sketch to be estimated passed in as bytes writable.
* @return the estimate of unique count from given sketch.
*/
public Double evaluate(final BytesWritable binarySketch) {
return evaluate(binarySketch, DEFAULT_UPDATE_SEED);
}
/**
* Returns the estimate unique count of sketch.
*
* @param binarySketch sketch to be estimated passed in as bytes writable.
* @param seed value used to build the sketch if different from the default
* @return the estimate of unique count from given sketch.
*/
public Double evaluate(final BytesWritable binarySketch, final long seed) {
if (binarySketch == null) {
return 0.0;
}
final byte[] serializedSketch = binarySketch.getBytes();
if (serializedSketch.length <= EMPTY_SKETCH_SIZE_BYTES) {
return 0.0;
}
return Sketch.wrap(Memory.wrap(serializedSketch), seed).getEstimate();
}
}