/* | |
* 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 a quantile value from a QuantilesSketch. A single value for a | |
* given fraction is returned. The fraction represents a normalized rank and must be | |
* from 0 to 1 inclusive. For example, the fraction of 0.5 corresponds to 50th percentile, | |
* which is the median value of the distribution (the number separating the higher half | |
* of the probability distribution from the lower half). | |
*/ | |
public class GetQuantile extends EvalFunc<Double> { | |
@Override | |
public Double exec(final Tuple input) throws IOException { | |
if (input.size() != 2) throw new IllegalArgumentException("expected two inputs: sketch and fraction"); | |
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())); | |
if (!(input.get(1) instanceof Double)) throw new IllegalArgumentException("expected a double value as a fraction, got " + input.get(1).getClass().getSimpleName()); | |
final double fraction = (double) input.get(1); | |
return sketch.getQuantile(fraction); | |
} | |
} |