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A module that is everything required to understands Druid Segments

There is a newer version: 0.12.3

/*
 * Licensed to Metamarkets Group Inc. (Metamarkets) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. Metamarkets 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 io.druid.query.aggregation;

import com.google.common.primitives.Longs;
import io.druid.segment.FloatColumnSelector;

import java.util.Comparator;

public class HistogramAggregator implements Aggregator
{
  static final Comparator COMPARATOR = new Comparator()
  {
    @Override
    public int compare(Object o, Object o1)
    {
      return Longs.compare(((Histogram) o).count, ((Histogram) o1).count);
    }
  };

  static Object combineHistograms(Object lhs, Object rhs) {
    return ((Histogram) lhs).fold((Histogram) rhs);
  }

  private final FloatColumnSelector selector;
  private final String name;

  private Histogram histogram;

  public HistogramAggregator(String name, FloatColumnSelector selector, float[] breaks) {
    this.name = name;
    this.selector = selector;
    this.histogram = new Histogram(breaks);
  }

  @Override
  public void aggregate()
  {
    histogram.offer(selector.get());
  }

  @Override
  public void reset()
  {
    this.histogram = new Histogram(histogram.breaks);
  }

  @Override
  public Object get()
  {
    return this.histogram;
  }

  @Override
  public float getFloat()
  {
    throw new UnsupportedOperationException("HistogramAggregator does not support getFloat()");
  }

  @Override
  public long getLong()
  {
    throw new UnsupportedOperationException("HistogramAggregator does not support getLong()");
  }

  @Override
  public String getName()
  {
    return name;
  }

  @Override
  public void close()
  {
    // no resources to cleanup
  }
}