src/main/java/org/apache/datasketches/hive/kll/GetCdfUDF.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
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 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
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package org.apache.datasketches.hive.kll;

import java.util.List;

import org.apache.datasketches.hive.common.BytesWritableHelper;
import org.apache.datasketches.kll.KllFloatsSketch;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.BytesWritable;

@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(BytesWritableHelper.wrapAsMemory(serializedSketch));
    final double[] cdf = sketch.getCDF(Util.objectsToPrimitives(splitPoints));
    if (cdf == null) { return null; }
    return Util.primitivesToList(cdf);
  }

}