皮尔逊相关系数JAVA实现

      经常需要计算皮尔森相关系数，在网上借鉴了算法和程序，不够理想，改进后，共享在这里，方便需要计算相关系数的使用。

import java.util.List;
/**
 * 计算两个样本数据之间的皮尔逊相关系数
 */
public class PearsonCorrelation {
	public static void main(String[] args) {
		test();
	}
	private static void test(){
		/*用于测试*/
		double[] x = new double[] { 0.98, 0.96, 0.96, 0.94, 0.925, 0.9025, 0.875 };
		double[] y = new double[] { 1, 1, 1, 1, 0.961483893, 0.490591662, 0.837341784 };
		double score = getPearsonCorrelationScore(x, y);
		System.out.println(score);//0.6350393282549671
	}

	public static double getPearsonCorrelationScore(List x, List y) {
		if (x.size() != y.size())
			throw new RuntimeException("数据不正确！");
		double[] xData = new double[x.size()];
		double[] yData = new double[x.size()];
		for (int i = 0; i < x.size(); i++) {
			xData[i] = x.get(i);
			yData[i] = y.get(i);
		}
		return getPearsonCorrelationScore(xData,yData);
	}

	public static double getPearsonCorrelationScore(double[] xData, double[] yData) {
		if (xData.length != yData.length)
			throw new RuntimeException("数据不正确！");
		double xMeans;
		double yMeans;
		double numerator = 0;// 求解皮尔逊的分子
		double denominator = 0;// 求解皮尔逊系数的分母

		double result = 0;
		// 拿到两个数据的平均值
		xMeans = getMeans(xData);
		yMeans = getMeans(yData);
		// 计算皮尔逊系数的分子
		numerator = generateNumerator(xData, xMeans, yData, yMeans);
		// 计算皮尔逊系数的分母
		denominator = generateDenomiator(xData, xMeans, yData, yMeans);
		// 计算皮尔逊系数
		result = numerator / denominator;
		return result;
	}

	/**
	 * 计算分子
	 * 
	 * @param xData
	 * @param xMeans
	 * @param yData
	 * @param yMeans
	 * @return
	 */
	private static double generateNumerator(double[] xData, double xMeans, double[] yData, double yMeans) {
		double numerator = 0.0;
		for (int i = 0; i < xData.length; i++) {
			numerator += (xData[i] - xMeans) * (yData[i] - yMeans);
		}
		return numerator;
	}

	/**
	 * 生成分母
	 * 
	 * @param yMeans
	 * @param yData
	 * @param xMeans
	 * @param xData
	 * @return 分母
	 */
	private static double generateDenomiator(double[] xData, double xMeans, double[] yData, double yMeans) {
		double xSum = 0.0;
		for (int i = 0; i < xData.length; i++) {
			xSum += (xData[i] - xMeans) * (xData[i] - xMeans);
		}
		double ySum = 0.0;
		for (int i = 0; i < yData.length; i++) {
			ySum += (yData[i] - yMeans) * (yData[i] - yMeans);
		}
		return Math.sqrt(xSum) * Math.sqrt(ySum);
	}

	/**
	 * 根据给定的数据集进行平均值计算
	 * 
	 * @param datas数据集
	 * @return 给定数据集的平均值
	 */
	private static double getMeans(double[] datas) {
		double sum = 0.0;
		for (int i = 0; i < datas.length; i++) {
			sum += datas[i];
		}
		return sum / datas.length;
	}
}