| /* |
| * Copyright 2019, Verizon Media. |
| * 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 = "GetCDF", |
| value = "_FUNC_(sketch, split points...)", |
| extended = "Returns an approximation to the Cumulative Distribution Function (CDF)" |
| + " 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 double valuess, the first M of which are approximations" |
| + " to the ranks of the corresponding split points (fraction of input stream values that are less" |
| + " than a split point). The last value is always 1." |
| + " CDF can also be viewed as a cumulative version of PMF.") |
| @SuppressWarnings("javadoc") |
| public class GetCdfUDF extends UDF { |
| |
| /** |
| * Returns a list of ranks (CDF) 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[] cdf = sketch.getCDF(Util.objectsToPrimitives(splitPoints)); |
| if (cdf == null) { return null; } |
| return Util.primitivesToList(cdf); |
| } |
| |
| } |