Java: 计算平均分, 标准差, 标准分

本类提供标准差,标准分计算的Utility.

/*
 * $Id$
 * Copyright (c) 2008-2010 ... Co. Ltd.
 * All Rights Reserved
 * Changelog:
 *   Li Guoliang - Jan 27, 2010: Initial version
 *
 */

package com...mgt;

import java.util.ArrayList;
import java.util.List;

/**
 * 考试成绩整合有关Utils
 * @author Li Guoliang
 *
 */
public class AssessConsolidateUtils {

	/**
	 * 为给定的分数列表计算对应的标准分, 返回对应的标准分列表.
	 * @param rawScores 原始分列表
	 * @return [平均分, 方差, 原始分对应的标准分列表(顺序同原始分列表)]
	 */
	public static Object[] calculateStandardScore(List rawScores) {
		List listStandardScore = new ArrayList();

		double scoreMean = calculateScoreMean(rawScores); // 1. 获得平均分
		// 2. 计算标准差
		double standardDeviation = calculateSTD(rawScores, scoreMean);

		for (int i = 0; i < rawScores.size(); i++) {
			double standardScore = (rawScores.get(i) - scoreMean)/standardDeviation;
			listStandardScore.add(i, standardScore); // 将标准分按顺序放入列表中.
		}

		Object[] consolidateValues = new Object[3];
		consolidateValues[0] = scoreMean;
		consolidateValues[1] = standardDeviation;
		consolidateValues[2] = listStandardScore;

		return consolidateValues;
	}

	/**
	 * 获得平均分.
	 * @param rawScores
	 * @return
	 */
	protected static double calculateScoreMean(List rawScores) {
		double scoreAll = 0.0;
		for (Double score : rawScores) {
			scoreAll += score;
		}
		return scoreAll/rawScores.size();
	}

	/**
	 * 计算标准差
	 * @param rawScores
	 * @param scoreMean
	 * @return
	 */
	protected static double calculateSTD(List rawScores, double scoreMean) {
		double allSquare = 0.0;
		for (Double rawScore : rawScores) {
			allSquare += (rawScore - scoreMean)*(rawScore - scoreMean);
		}
		// (xi - x(平均分)的平方 的和计算完毕
		double denominator = rawScores.size() * (rawScores.size() - 1);
		return Math.sqrt(allSquare/denominator);
	}
}