src/main/java/org/apache/datasketches/hive/hll/UnionSketchUDF.java

/*
 * 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.hll;

import org.apache.datasketches.hive.common.BytesWritableHelper;
import org.apache.datasketches.hll.HllSketch;
import org.apache.datasketches.hll.TgtHllType;
import org.apache.datasketches.hll.Union;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.BytesWritable;

/**
 * Hive union sketch UDF.
 */
@Description(
    name = "unionSketch",
    value = "_FUNC_(firstSketch, secondSketch[, lgK[, type]]) - Compute the union of the given "
        + "sketches with the given size and seed",
    extended = "The return value is a binary blob that can be operated on by other sketch related functions."
        + " The lgK parameter controls the sketch size and relative error expected from the sketch."
        + " It is optional and must be from 4 to 21. The default is 12, which is expected to yield errors"
        + " of roughly +-3% in the estimation of uniques with 95% confidence."
        + " The target type parameter is optional and must be 'HLL_4', 'HLL_6' or 'HLL_8'."
        + " The default is 'HLL_4'")
@SuppressWarnings("deprecation")
public class UnionSketchUDF extends UDF {

  /**
   * Union two sketches given explicit lgK and target HLL type
   *
   * @param firstSketch
   *   first sketch to be unioned.
   * @param secondSketch
   *          second sketch to be unioned.
   * @param lgK
   *   final output lgK
   *   This must be between 4 and 21.
   * @param type
   *   final output HLL type
   * @return resulting sketch of union.
   */
  public BytesWritable evaluate(final BytesWritable firstSketch, final BytesWritable secondSketch,
      final int lgK, final String type) {

    final TgtHllType hllType = TgtHllType.valueOf(type);
    final Union union = new Union(lgK);

    if (firstSketch != null) {
      union.update(HllSketch.wrap(BytesWritableHelper.wrapAsMemory(firstSketch)));
    }

    if (secondSketch != null) {
      union.update(HllSketch.wrap(BytesWritableHelper.wrapAsMemory(secondSketch)));
    }

    return new BytesWritable(union.getResult(hllType).toCompactByteArray());
  }

  /**
   * Union two sketches given explicit lgK and using default target HLL type
   *
   * @param firstSketch
   *   first sketch to be unioned.
   * @param secondSketch
   *   second sketch to be unioned.
   * @param lgK
   *   final output lgK
   *   This must be between 4 and 21.
   * @return resulting sketch of union.
   */
  public BytesWritable evaluate(final BytesWritable firstSketch, final BytesWritable secondSketch,
      final int lgK) {
    return evaluate(firstSketch, secondSketch, lgK, SketchEvaluator.DEFAULT_HLL_TYPE.toString());
  }

  /**
   * Union two sketches using default lgK an target HLL type
   *
   * @param firstSketch
   *          first sketch to be unioned.
   * @param secondSketch
   *          second sketch to be unioned.
   * @return resulting sketch of union.
   */
  public BytesWritable evaluate(final BytesWritable firstSketch, final BytesWritable secondSketch) {
    return evaluate(firstSketch, secondSketch, SketchEvaluator.DEFAULT_LG_K,
        SketchEvaluator.DEFAULT_HLL_TYPE.toString());
  }

}