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Apache Hive adaptors for the DataSketches library.

There is a newer version: 2.0.0

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * 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,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.datasketches.hive.quantiles;

import java.util.Comparator;
import java.util.List;

import org.apache.datasketches.ArrayOfStringsSerDe;
import org.apache.datasketches.hive.common.BytesWritableHelper;
import org.apache.datasketches.quantiles.ItemsSketch;
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 domain 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("deprecation")
public class GetCdfFromStringsSketchUDF 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 evaluate(final BytesWritable serializedSketch, final String... splitPoints) {
    if (serializedSketch == null) { return null; }
    final ItemsSketch sketch = ItemsSketch.getInstance(
      BytesWritableHelper.wrapAsMemory(serializedSketch),
      Comparator.naturalOrder(),
      new ArrayOfStringsSerDe()
    );
    final double[] cdf = sketch.getCDF(splitPoints);
    if (cdf == null) { return null; }
    return Util.primitivesToList(cdf);
  }

}