com.yahoo.sketches.hive.quantiles.GetPmfFromDoublesSketchUDF Maven / Gradle / Ivy
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/*
* 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.quantiles;
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.quantiles.DoublesSketch;
@Description(
name = "GetPMF",
value = "_FUNC_(sketch, split points...)",
extended = "Returns an approximation to the Probability Mass Function (PMF)"
+ " from a sketch given a set of split points (values)."
+ " Split points are an array of M unique, monotonically increasing values"
+ " that divide the real number line into M+1 consecutive disjoint intervals."
+ " The function returns an array of M+1 doubles, each of which is an approximation"
+ " to the fraction of the values that fell into one of those intervals."
+ " The definition of an interval is inclusive of the left split point and exclusive"
+ " of the right split point")
public class GetPmfFromDoublesSketchUDF extends UDF {
/**
* Returns a list of fractions (PMF) from a given sketch
* @param serializedSketch serialized sketch
* @param splitPoints list of unique and monotonically increasing values
* @return list of fractions from 0 to 1
*/
public List evaluate(final BytesWritable serializedSketch, final Double... splitPoints) {
if (serializedSketch == null) { return null; }
final DoublesSketch sketch = DoublesSketch.wrap(Memory.wrap(serializedSketch.getBytes()));
final double[] pmf = sketch.getPMF(Util.objectsToPrimitives(splitPoints));
if (pmf == null) { return null; }
return Util.primitivesToList(pmf);
}
}