com.yahoo.sketches.pig.quantiles.GetPmfFromStringsSketch Maven / Gradle / Ivy
/*
* 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 java.util.Comparator;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.DataByteArray;
import org.apache.pig.data.Tuple;
import com.yahoo.memory.Memory;
import com.yahoo.sketches.ArrayOfStringsSerDe;
import com.yahoo.sketches.quantiles.ItemsSketch;
/**
* 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 m unique, monotonically increasing
* values that divide the domain 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 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 GetPmfFromStringsSketch extends EvalFunc {
@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 ItemsSketch sketch =
ItemsSketch.getInstance(Memory.wrap(dba.get()), Comparator.naturalOrder(),
new ArrayOfStringsSerDe());
final String[] splitPoints = new String[input.size() - 1];
for (int i = 1; i < input.size(); i++) {
if (!(input.get(i) instanceof String)) {
throw new IllegalArgumentException("expected a string value as a split point, got "
+ input.get(i).getClass().getSimpleName());
}
splitPoints[i - 1] = (String) input.get(i);
}
return Util.doubleArrayToTuple(sketch.getPMF(splitPoints));
}
}