src/main/java/com/yahoo/sketches/hive/theta/EstimateSketchUDF.java

/*
 * 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.hive.theta;

import static com.yahoo.sketches.Util.DEFAULT_UPDATE_SEED;

import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.BytesWritable;

import com.yahoo.memory.Memory;
import com.yahoo.sketches.theta.Sketch;

/**
 * Hive estimate sketch udf. V4
 *
 */
public class EstimateSketchUDF extends UDF {

  private static final int EMPTY_SKETCH_SIZE_BYTES = 8;

  /**
   * Returns the estimate unique count of sketch.
   *
   * @param binarySketch sketch to be estimated passed in as bytes writable.
   * @return the estimate of unique count from given sketch.
   */
  public Double evaluate(final BytesWritable binarySketch) {
    return evaluate(binarySketch, DEFAULT_UPDATE_SEED);
  }

  /**
   * Returns the estimate unique count of sketch.
   *
   * @param binarySketch sketch to be estimated passed in as bytes writable.
   * @param seed value used to build the sketch if different from the default
   * @return the estimate of unique count from given sketch.
   */
  public Double evaluate(final BytesWritable binarySketch, final long seed) {
    if (binarySketch == null) {
      return 0.0;
    }

    final byte[] serializedSketch = binarySketch.getBytes();

    if (serializedSketch.length <= EMPTY_SKETCH_SIZE_BYTES) {
      return 0.0;
    }

    return Sketch.wrap(Memory.wrap(serializedSketch), seed).getEstimate();
  }

}