从数字列表中查找标准差（用户输入）

Question

我尝试寻找一个示例，说明如何从用户输入的数量列表中找到标准偏差。我想知道是否有人可以解释如何从扫描仪中找到数字列表的标准偏差。任何建议都会很棒。

-提前致谢

Answer 1

当然——这样就可以了。

package statistics;

/**
 * Statistics
 * @author Michael
 * @link http://stackoverflow.com/questions/11978667/online-algorithm-for-calculating-standrd-deviation/11978689#11978689
 * @link http://mathworld.wolfram.com/Variance.html
 * @since 8/15/12 7:34 PM
 */
public class Statistics {

    private int n;
    private double sum;
    private double sumsq;

    public void reset() {
        this.n = 0;
        this.sum = 0.0;
        this.sumsq = 0.0;
    }

    public synchronized void addValue(double x) {
        ++this.n;
        this.sum += x;
        this.sumsq += x*x;
    }

    public synchronized double calculateMean() {
        double mean = 0.0;
        if (this.n > 0) {
            mean = this.sum/this.n;
        }
        return mean;
    }

    public synchronized double calculateVariance() {
        double variance = 0.0;
        if (this.n > 0) {
            variance = Math.sqrt(this.sumsq-this.sum*this.sum/this.n)/this.n;
        }
        return variance;
    }

    public synchronized double calculateStandardDeviation() {
        double deviation = 0.0;
        if (this.n > 1) {
            deviation = Math.sqrt((this.sumsq-this.sum*this.sum/this.n)/(this.n-1));
        }
        return deviation;
    }
}