/**皮爾遜相關係數
 *
ρ =(∑xy - ∑x∑y/n)/(∑x^2 - (∑x)^2/n)(∑y^2-(∑y)^2/n)^0.5
 */
public class PersonCorrelationCoefficient {

    public double personCoefficient(Instance a,Instance b){
        if (a.noAttributes() != b.noAttributes())
            throw new RuntimeException("兩個資料例項的屬性數目不一致");
        double xy =0;
        double
 
 sumX = 0;
        double sumY = 0;
        double xTo = 0;
        double yTo =0;
        for (int i=0;i<a.noAttributes();i++){
            xy += a.value(i) * b.value(i);
            sumX += a.value(i);
            sumY += b.value(i);
            xTo += a.value(i) * a.value(i);
            yTo += b.value
 
(i) * b.value(i);
        }
        int n = a.noAttributes();
        return (xy - (sumX * sumY) / n)
                / Math.sqrt((xTo-(sumX * sumX)/n)*(yTo - (sumY * sumY) / n));
    }
}