com.google.cloud.dataflow.sdk.transforms.windowing.MergeOverlappingIntervalWindows Maven / Gradle / Ivy

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Google Cloud Dataflow Java SDK provides a simple, Java-based interface for processing virtually any size data using Google cloud resources. This artifact includes entire Dataflow Java SDK.

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/*
 * Copyright (C) 2015 Google Inc.
 *
 * Licensed 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 com.google.cloud.dataflow.sdk.transforms.windowing;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * A utility function for merging overlapping {@link IntervalWindow}s.
 */
public class MergeOverlappingIntervalWindows {

  /**
   * Merge overlapping {@link IntervalWindow}s.
   */
  public static void mergeWindows(WindowFn.MergeContext c) throws Exception {
    // Merge any overlapping windows into a single window.
    // Sort the list of existing windows so we only have to
    // traverse the list once rather than considering all
    // O(n^2) window pairs.
    List sortedWindows = new ArrayList<>();
    for (IntervalWindow window : c.windows()) {
      sortedWindows.add(window);
    }
    Collections.sort(sortedWindows);
    List merges = new ArrayList<>();
    MergeCandidate current = new MergeCandidate();
    for (IntervalWindow window : sortedWindows) {
      if (current.intersects(window)) {
        current.add(window);
      } else {
        merges.add(current);
        current = new MergeCandidate(window);
      }
    }
    merges.add(current);
    for (MergeCandidate merge : merges) {
      merge.apply(c);
    }
  }

  private static class MergeCandidate {
    private IntervalWindow union;
    private final List parts;
    public MergeCandidate() {
      parts = new ArrayList<>();
    }
    public MergeCandidate(IntervalWindow window) {
      union = window;
      parts = new ArrayList<>(Arrays.asList(window));
    }
    public boolean intersects(IntervalWindow window) {
      return union == null || union.intersects(window);
    }
    public void add(IntervalWindow window) {
      union = union == null ? window : union.span(window);
      parts.add(window);
    }
    public void apply(WindowFn.MergeContext c) throws Exception {
      if (parts.size() > 1) {
        c.merge(parts, union);
      }
    }

    @Override
    public String toString() {
      return "MergeCandidate[union=" + union + ", parts=" + parts + "]";
    }
  }
}