001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.math3.stat.descriptive.rank;
018
019import java.io.Serializable;
020
021import org.apache.commons.math3.exception.MathIllegalArgumentException;
022import org.apache.commons.math3.exception.NullArgumentException;
023import org.apache.commons.math3.stat.ranking.NaNStrategy;
024import org.apache.commons.math3.util.KthSelector;
025
026
027/**
028 * Returns the median of the available values.  This is the same as the 50th percentile.
029 * See {@link Percentile} for a description of the algorithm used.
030 * <p>
031 * <strong>Note that this implementation is not synchronized.</strong> If
032 * multiple threads access an instance of this class concurrently, and at least
033 * one of the threads invokes the <code>increment()</code> or
034 * <code>clear()</code> method, it must be synchronized externally.</p>
035 *
036 */
037public class Median extends Percentile implements Serializable {
038
039    /** Serializable version identifier */
040    private static final long serialVersionUID = -3961477041290915687L;
041
042    /** Fixed quantile. */
043    private static final double FIXED_QUANTILE_50 = 50.0;
044
045    /**
046     * Default constructor.
047     */
048    public Median() {
049        // No try-catch or advertised exception - arg is valid
050        super(FIXED_QUANTILE_50);
051    }
052
053    /**
054     * Copy constructor, creates a new {@code Median} identical
055     * to the {@code original}
056     *
057     * @param original the {@code Median} instance to copy
058     * @throws NullArgumentException if original is null
059     */
060    public Median(Median original) throws NullArgumentException {
061        super(original);
062    }
063
064    /**
065     * Constructs a Median with the specific {@link EstimationType}, {@link NaNStrategy} and {@link PivotingStrategy}.
066     *
067     * @param estimationType one of the percentile {@link EstimationType  estimation types}
068     * @param nanStrategy one of {@link NaNStrategy} to handle with NaNs
069     * @param kthSelector {@link KthSelector} to use for pivoting during search
070     * @throws MathIllegalArgumentException if p is not within (0,100]
071     * @throws NullArgumentException if type or NaNStrategy passed is null
072     */
073    private Median(final EstimationType estimationType, final NaNStrategy nanStrategy,
074                   final KthSelector kthSelector)
075        throws MathIllegalArgumentException {
076        super(FIXED_QUANTILE_50, estimationType, nanStrategy, kthSelector);
077    }
078
079    /** {@inheritDoc} */
080    @Override
081    public Median withEstimationType(final EstimationType newEstimationType) {
082        return new Median(newEstimationType, getNaNStrategy(), getKthSelector());
083    }
084
085    /** {@inheritDoc} */
086    @Override
087    public Median withNaNStrategy(final NaNStrategy newNaNStrategy) {
088        return new Median(getEstimationType(), newNaNStrategy, getKthSelector());
089    }
090
091    /** {@inheritDoc} */
092    @Override
093    public Median withKthSelector(final KthSelector newKthSelector) {
094        return new Median(getEstimationType(), getNaNStrategy(), newKthSelector);
095    }
096
097}