/* | |
* 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.pig.quantiles; | |
import java.io.IOException; | |
import org.apache.pig.EvalFunc; | |
import org.apache.pig.data.DataByteArray; | |
import org.apache.pig.data.Tuple; | |
import com.yahoo.sketches.memory.NativeMemory; | |
import com.yahoo.sketches.quantiles.QuantilesSketch; | |
/** | |
* This UDF is to get an approximation to the Probability Mass Function (PMF) of the input stream | |
* given a sketch and a set of split points - an array of <i>m</i> unique, monotonically increasing | |
* double values that divide the real number line into <i>m+1</i> consecutive disjoint intervals. | |
* The function returns an array of m+1 doubles each of which is an approximation to the fraction | |
* of the input stream values that fell into one of those intervals. Intervals are inclusive of | |
* the left split point and exclusive of the right split point. | |
*/ | |
public class GetPMF extends EvalFunc<Tuple> { | |
@Override | |
public Tuple exec(final Tuple input) throws IOException { | |
if (input.size() < 2) throw new IllegalArgumentException("expected two or more inputs: sketch and list of split points"); | |
if (!(input.get(0) instanceof DataByteArray)) throw new IllegalArgumentException("expected a DataByteArray as a sketch, got " + input.get(0).getClass().getSimpleName()); | |
final DataByteArray dba = (DataByteArray) input.get(0); | |
final QuantilesSketch sketch = QuantilesSketch.heapify(new NativeMemory(dba.get())); | |
double[] splitPoints = new double[input.size() - 1]; | |
for (int i = 1; i < input.size(); i++) { | |
if (!(input.get(i) instanceof Double)) throw new IllegalArgumentException("expected a double value as a split point, got " + input.get(i).getClass().getSimpleName()); | |
splitPoints[i - 1] = (double) input.get(i); | |
} | |
return Util.doubleArrayToTuple(sketch.getPMF(splitPoints)); | |
} | |
} |