org.codelibs.elasticsearch.taste.common.WeightedRunningAverage Maven / Gradle / Ivy

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/**
 * 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.codelibs.elasticsearch.taste.common;

import java.io.Serializable;

import com.google.common.base.Preconditions;

public class WeightedRunningAverage implements RunningAverage, Serializable {

    /**
     *
     */
    private static final long serialVersionUID = 1L;

    private double totalWeight;

    private double average;

    public WeightedRunningAverage() {
        totalWeight = 0.0;
        average = Double.NaN;
    }

    @Override
    public synchronized void addDatum(final double datum) {
        addDatum(datum, 1.0);
    }

    public synchronized void addDatum(final double datum, final double weight) {
        final double oldTotalWeight = totalWeight;
        totalWeight += weight;
        if (oldTotalWeight <= 0.0) {
            average = datum;
        } else {
            average = average * oldTotalWeight / totalWeight + datum * weight
                    / totalWeight;
        }
    }

    @Override
    public synchronized void removeDatum(final double datum) {
        removeDatum(datum, 1.0);
    }

    public synchronized void removeDatum(final double datum, final double weight) {
        final double oldTotalWeight = totalWeight;
        totalWeight -= weight;
        if (totalWeight <= 0.0) {
            average = Double.NaN;
            totalWeight = 0.0;
        } else {
            average = average * oldTotalWeight / totalWeight - datum * weight
                    / totalWeight;
        }
    }

    @Override
    public synchronized void changeDatum(final double delta) {
        changeDatum(delta, 1.0);
    }

    public synchronized void changeDatum(final double delta, final double weight) {
        Preconditions.checkArgument(weight <= totalWeight,
                "weight must be <= totalWeight");
        average += delta * weight / totalWeight;
    }

    public synchronized double getTotalWeight() {
        return totalWeight;
    }

    /** @return {@link #getTotalWeight()} */
    @Override
    public synchronized int getCount() {
        return (int) totalWeight;
    }

    @Override
    public synchronized double getAverage() {
        return average;
    }

    @Override
    public RunningAverage inverse() {
        return new InvertedRunningAverage(this);
    }

    @Override
    public synchronized String toString() {
        return String.valueOf(average);
    }

}