com.yahoo.sketches.hive.tuple.ArrayOfDoublesSketchToVariancesUDF Maven / Gradle / Ivy
/*
* Copyright 2017, 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.hive.tuple;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.math3.stat.descriptive.SummaryStatistics;
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.tuple.ArrayOfDoublesSketch;
import com.yahoo.sketches.tuple.ArrayOfDoublesSketches;
@Description(
name = "ArrayOfDoublesSketchToVariances",
value = "_FUNC_(sketch)",
extended = "Returns a list of variance values from a given ArrayOfDoublesSketch."
+ " The result will be N double values, where N is the number of double values kept in the"
+ " sketch per key.")
public class ArrayOfDoublesSketchToVariancesUDF extends UDF {
/**
* Get variances from a given ArrayOfDoublesSketch
* @param serializedSketch ArrayOfDoublesSketch in as serialized binary
* @return list of variances
*/
public List evaluate(final BytesWritable serializedSketch) {
if (serializedSketch == null) { return null; }
final ArrayOfDoublesSketch sketch = ArrayOfDoublesSketches.wrapSketch(
Memory.wrap(serializedSketch.getBytes()));
if (sketch.getRetainedEntries() < 1) {
return null;
}
final SummaryStatistics[] summaries = ArrayOfDoublesSketchStats.sketchToSummaryStatistics(sketch);
final List variances = new ArrayList(sketch.getNumValues());
for (int i = 0; i < sketch.getNumValues(); i++) {
variances.add(summaries[i].getVariance());
}
return variances;
}
}