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Core sketch algorithms used alone and by other Java repositories in the DataSketches library.
There is a newer version: 7.0.0
/*
 * 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.tuple;

import static org.apache.datasketches.Util.LS;

import org.apache.datasketches.BinomialBoundsN;

/**
 * This is an equivalent to org.apache.datasketches.theta.Sketch with
 * addition of a user-defined Summary object associated with every unique entry
 * in the sketch.
 * @param  Type of Summary
 */
public abstract class Sketch {

  protected static final byte PREAMBLE_LONGS = 1;

  long[] keys_;
  S[] summaries_;
  long theta_;
  boolean isEmpty_ = true;

  Sketch() {}

  /**
   * Estimates the cardinality of the set (number of unique values presented to the sketch)
   * @return best estimate of the number of unique values
   */
  public double getEstimate() {
    if (!isEstimationMode()) { return getRetainedEntries(); }
    return getRetainedEntries() / getTheta();
  }

  /**
   * Gets the approximate upper error bound given the specified number of Standard Deviations.
   * This will return getEstimate() if isEmpty() is true.
   *
   * @param numStdDev
   * See Number of Standard Deviations
   * @return the upper bound.
   */
  public double getUpperBound(final int numStdDev) {
    if (!isEstimationMode()) { return getRetainedEntries(); }
    return BinomialBoundsN.getUpperBound(getRetainedEntries(), getTheta(), numStdDev, isEmpty_);
  }

  /**
   * Gets the approximate lower error bound given the specified number of Standard Deviations.
   * This will return getEstimate() if isEmpty() is true.
   *
   * @param numStdDev
   * See Number of Standard Deviations
   * @return the lower bound.
   */
  public double getLowerBound(final int numStdDev) {
    if (!isEstimationMode()) { return getRetainedEntries(); }
    return BinomialBoundsN.getLowerBound(getRetainedEntries(), getTheta(), numStdDev, isEmpty_);
  }

  /**
   * See Empty
   * @return true if empty.
   */
  public boolean isEmpty() {
    return isEmpty_;
  }

  /**
   * Returns true if the sketch is Estimation Mode (as opposed to Exact Mode).
   * This is true if theta < 1.0 AND isEmpty() is false.
   * @return true if the sketch is in estimation mode.
   */
  public boolean isEstimationMode() {
    return ((theta_ < Long.MAX_VALUE) && !isEmpty());
  }

  /**
   * @return number of retained entries
   */
  public abstract int getRetainedEntries();

  /**
   * Gets the value of theta as a double between zero and one
   * @return the value of theta as a double
   */
  public double getTheta() {
    return theta_ / (double) Long.MAX_VALUE;
  }

  /**
   * This is to serialize an instance to a byte array.
   * @return serialized representation of the sketch
   */
  public abstract byte[] toByteArray();

  /**
   * Returns a SketchIterator
   * @return a SketchIterator
   */
  public SketchIterator iterator() {
    return new SketchIterator<>(keys_, summaries_);
  }

  /**
   * Returns Theta as a long
   * @return Theta as a long
   */
  public long getThetaLong() {
    return theta_;
  }

  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder();
    sb.append("### ").append(this.getClass().getSimpleName()).append(" SUMMARY: ").append(LS);
    sb.append("   Estimate                : ").append(getEstimate()).append(LS);
    sb.append("   Upper Bound, 95% conf   : ").append(getUpperBound(2)).append(LS);
    sb.append("   Lower Bound, 95% conf   : ").append(getLowerBound(2)).append(LS);
    sb.append("   Theta (double)          : ").append(this.getTheta()).append(LS);
    sb.append("   Theta (long)            : ").append(this.getThetaLong()).append(LS);
    sb.append("   EstMode?                : ").append(isEstimationMode()).append(LS);
    sb.append("   Empty?                  : ").append(isEmpty()).append(LS);
    sb.append("   Retained Entries        : ").append(this.getRetainedEntries()).append(LS);
    if (this instanceof UpdatableSketch) {
      @SuppressWarnings("rawtypes")
      final UpdatableSketch updatable = (UpdatableSketch) this;
      sb.append("   Nominal Entries (k)     : ").append(updatable.getNominalEntries()).append(LS);
      sb.append("   Current Capacity        : ").append(updatable.getCurrentCapacity()).append(LS);
      sb.append("   Resize Factor           : ").append(updatable.getResizeFactor().getValue()).append(LS);
      sb.append("   Sampling Probability (p): ").append(updatable.getSamplingProbability()).append(LS);
    }
    sb.append("### END SKETCH SUMMARY").append(LS);
    return sb.toString();
  }

}