| /* |
| * Copyright 2018, Oath 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.kll; |
| |
| 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.kll.KllFloatsSketch; |
| |
| @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 GetPmfUDF 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<Double> evaluate(final BytesWritable serializedSketch, final Float... splitPoints) { |
| if (serializedSketch == null) { return null; } |
| final KllFloatsSketch sketch = KllFloatsSketch.heapify(Memory.wrap(serializedSketch.getBytes())); |
| final double[] pmf = sketch.getPMF(Util.objectsToPrimitives(splitPoints)); |
| if (pmf == null) { return null; } |
| return Util.primitivesToList(pmf); |
| } |
| |
| } |