statistics.java

java图形利器

/* ===========================================================
 * JFreeChart : a free chart library for the Java(tm) platform
 * ===========================================================
 *
 * (C) Copyright 2000-2006, by Object Refinery Limited and Contributors.
 *
 * Project Info:  http://www.jfree.org/jfreechart/index.html
 *
 * This library is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU Lesser General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA.  
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 *
 * ---------------
 * Statistics.java
 * ---------------
 * (C) Copyright 2000-2006, by Matthew Wright and Contributors.
 *
 * Original Author:  Matthew Wright;
 * Contributor(s):   David Gilbert (for Object Refinery Limited);
 *
 * $Id: Statistics.java,v 1.5.2.2 2006/11/16 11:19:47 mungady Exp $
 *
 * Changes (from 08-Nov-2001)
 * --------------------------
 * 08-Nov-2001 : Added standard header and tidied Javadoc comments (DG);
 *               Moved from JFreeChart to package com.jrefinery.data.* in 
 *               JCommon class library (DG);
 * 24-Jun-2002 : Removed unnecessary local variable (DG);
 * 07-Oct-2002 : Fixed errors reported by Checkstyle (DG);
 * 26-May-2004 : Moved calculateMean() method from BoxAndWhiskerCalculator (DG);
 * 02-Jun-2004 : Fixed bug in calculateMedian() method (DG);
 * 11-Jan-2005 : Removed deprecated code in preparation for the 1.0.0 
 *               release (DG);
 *
 */

package org.jfree.data.statistics;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

/**
 * A utility class that provides some common statistical functions.
 */
public abstract class Statistics {

    /**
     * Returns the mean of an array of numbers.  This is equivalent to calling
     * <code>calculateMean(values, true)</code>.
     *
     * @param values  the values (<code>null</code> not permitted).
     *
     * @return The mean.
     */
    public static double calculateMean(Number[] values) {
        return calculateMean(values, true);
    }
    
    /**
     * Returns the mean of an array of numbers.
     *
     * @param values  the values (<code>null</code> not permitted).
     * @param includeNullAndNaN  a flag that controls whether or not 
     *     <code>null</code> and <code>Double.NaN</code> values are included
     *     in the calculation (if either is present in the array, the result is 
     *     {@link Double#NaN}).
     *
     * @return The mean.
     * 
     * @since 1.0.3
     */
    public static double calculateMean(Number[] values, 
            boolean includeNullAndNaN) {
        
        if (values == null) {
            throw new IllegalArgumentException("Null 'values' argument.");
        }
        double sum = 0.0;
        double current;
        int counter = 0;
        for (int i = 0; i < values.length; i++) {
            // treat nulls the same as NaNs
            if (values[i] != null) {
                current = values[i].doubleValue();    
            }
            else {
                current = Double.NaN;
            }
            // calculate the sum and count
            if (includeNullAndNaN || !Double.isNaN(current)) {
                sum = sum + current;
                counter++;
            }
        }
        double result = (sum / counter);
        return result;
    }

    /**
     * Returns the mean of a collection of <code>Number</code> objects.
     * 
     * @param values  the values (<code>null</code> not permitted).
     * 
     * @return The mean.
     */
    public static double calculateMean(Collection values) {
        return calculateMean(values, true);
    }
    
    /**
     * Returns the mean of a collection of <code>Number</code> objects.
     * 
     * @param values  the values (<code>null</code> not permitted).
     * @param includeNullAndNaN  a flag that controls whether or not 
     *     <code>null</code> and <code>Double.NaN</code> values are included
     *     in the calculation (if either is present in the array, the result is 
     *     {@link Double#NaN}).
     * 
     * @return The mean.
     * 
     * @since 1.0.3
     */
    public static double calculateMean(Collection values, 
            boolean includeNullAndNaN) {
        
        if (values == null) {
            throw new IllegalArgumentException("Null 'values' argument.");
        }
        int count = 0;
        double total = 0.0;
        Iterator iterator = values.iterator();
        while (iterator.hasNext()) {
            Object object = iterator.next();
            if (object == null) {
                if (includeNullAndNaN) {
                    return Double.NaN;
                }
            }
            else {
                if (object instanceof Number) {
                    Number number = (Number) object;
                    double value = number.doubleValue();
                    if (Double.isNaN(value)) {
                        if (includeNullAndNaN) {
                            return Double.NaN;
                        }
                    }
                    else {
                        total = total + number.doubleValue();
                        count = count + 1;
                    }
                }
            }
        }      
        return total / count;
    }

    /**
     * Calculates the median for a list of values (<code>Number</code> objects).
     * The list of values will be copied, and the copy sorted, before 
     * calculating the median.  To avoid this step (if your list of values
     * is already sorted), use the {@link #calculateMedian(List, boolean)} 
     * method.
     * 
     * @param values  the values (<code>null</code> permitted).
     * 
     * @return The median.
     */
    public static double calculateMedian(List values) {
        return calculateMedian(values, true);
    }
    
    /**
     * Calculates the median for a list of values (<code>Number</code> objects).
     * If <code>copyAndSort</code> is <code>false</code>, the list is assumed
     * to be presorted in ascending order by value.
     * 
     * @param values  the values (<code>null</code> permitted).
     * @param copyAndSort  a flag that controls whether the list of values is
     *                     copied and sorted.
     * 
     * @return The median.
     */
    public static double calculateMedian(List values, boolean copyAndSort) {
        
        double result = Double.NaN;
        if (values != null) {
            if (copyAndSort) {
                int itemCount = values.size();
                List copy = new ArrayList(itemCount);
                for (int i = 0; i < itemCount; i++) {
                    copy.add(i, values.get(i));   
                }
                Collections.sort(copy);
                values = copy;
            }
            int count = values.size();
            if (count > 0) {
                if (count % 2 == 1) {
                    if (count > 1) {
                        Number value = (Number) values.get((count - 1) / 2);
                        result = value.doubleValue();
                    }
                    else {
                        Number value = (Number) values.get(0);
                        result = value.doubleValue();
                    }
                }
                else {
                    Number value1 = (Number) values.get(count / 2 - 1);
                    Number value2 = (Number) values.get(count / 2);
                    result = (value1.doubleValue() + value2.doubleValue()) 
                             / 2.0;
                }
            }
        }
        return result;
    }
    
    /**
     * Calculates the median for a sublist within a list of values 
     * (<code>Number</code> objects).
     * 
     * @param values  the values, in any order (<code>null</code> not 
     *                permitted).
     * @param start  the start index.
     * @param end  the end index.
     * 
     * @return The median.
     */