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Data Sketches Core

There is a newer version: 0.13.4

/*
 * Copyright 2015-16, 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.tuple;

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

/**
 * Compute a union of two or more tuple sketches.
 * A new instance represents an empty set.
 * Every update() computes a union with the internal set
 * and can only grow the internal set.
 * @param  Type of Summary
 */
public class Union {
  private final int nomEntries_;
  private final SummaryFactory summaryFactory_;
  private QuickSelectSketch sketch_;
  private long theta_; // need to maintain outside of the sketch

  /**
   * Creates new instance with default nominal entries
   * @param summaryFactory the summary factory
   */
  public Union(final SummaryFactory summaryFactory) {
    this(DEFAULT_NOMINAL_ENTRIES, summaryFactory);
  }

  /**
   * Creates new instance
   * @param nomEntries nominal number of entries. Forced to the nearest power of 2 greater than
   * given value.
   * @param summaryFactory the summary factory
   */
  public Union(final int nomEntries, final SummaryFactory summaryFactory) {
    nomEntries_ = nomEntries;
    summaryFactory_ = summaryFactory;
    sketch_ = new QuickSelectSketch(nomEntries, summaryFactory);
    theta_ = sketch_.getThetaLong();
  }

  /**
   * Updates the internal set by adding entries from the given sketch
   * @param sketchIn input sketch to add to the internal set
   */
  public void update(final Sketch sketchIn) {
    if (sketchIn == null || sketchIn.isEmpty()) { return; }
    if (sketchIn.theta_ < theta_) { theta_ = sketchIn.theta_; }
    final SketchIterator it = sketchIn.iterator();
    while (it.next()) {
      sketch_.merge(it.getKey(), it.getSummary());
    }
  }

  /**
   * Gets the internal set as a CompactSketch
   * @return result of the unions so far
   */
  public CompactSketch getResult() {
    sketch_.trim();
    if (theta_ < sketch_.theta_) {
      sketch_.setThetaLong(theta_);
      sketch_.rebuild();
    }
    return sketch_.compact();
  }

  /**
   * Resets the internal set to the initial state, which represents an empty set
   */
  public void reset() {
    sketch_ = new QuickSelectSketch(nomEntries_, summaryFactory_);
  }
}