未输出正确的均值或方差

Question

我的任务是取数字，每行一个，然后计算平均值、中位数、方差和标准差。当输入 null 或输入 500 个数字时，while 循环停止。我计算了中位数和标准差，但由于某种原因，我的方差和均值输出是错误的。另外，如果您可以帮助我设置 while 循环的参数，以便在输入 500 个数字时也结束。

我的意见：

0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0, 1.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 3.0, 3.0, 3.0, 3.0, 3.0, 4.0 , 4.0, 4.0, 4.0, 5.0, 5.0, 5.0, 5.0, 5.0, 5.0, 5.0, 5.0, 5.0, 6.0, 6.0, 6.0, 6.0, 7.0, 7.0, 7.0, 7.0, 7.0, 8.0, 8.0, 8.0, 8.0 , 8.0, 8.0, 8.0, 9.0, 9.0, 9.0, 9.0, 9.0, 9.0, 9.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 11.0, 11.0, 11.0, 11.0, 11.0, 11.0, 12.2. ，12.0,12.0,12.0,13.0,12.0,13.0,13.0,13.0,13.0,13.0,13.0,13.0,13.0,13.0,14.0,14.0,14.0,14.0,14.0,14.0,15.0,15.0,15.0,15.0,15.0 ，15.0,15.0,16.0,16.0,16.0,17.0,17.0,17.0,17.0,18.0,18.0,18.0,18.0,18.0,18.0,18.0,19.0,19.0,19.0,19.0,19.0,19.0,20.0,20.0,19.0,20.0,20.0,120.0,20.0,20.0,20.0,20.0,20.0,20.0,20.0,20.0,20.0 ，20.0,21.0,21.0,21.0,21.0,21.0,21.0,21.0,21.0,22.0,22.0,22.0,22.0,22.0,22.0,22.0,22.0,22.0,22.0,23.0,23.0,23.0,23.0,23.0,23.0,23.0,23.0,24.0,23.0,23.0,24.0,24.0,23.0,24.0,24.0,24.0,24.0 ，24.0,25.0,25.0,25.0,25.0,25.0,25.0,26.0,26.0,26.0,26.0,26.0,26.0,26.0,26.0,27.0,27.0,27.0,27.0,27.0,27.0,28.0,28.0,28.0,29.0,28.0,28.0,29.0,29.0,28.0,29.0,29.0,29.0,29.0,29.0,29.0,29.0 , 29.0, 30.0, 30.0,30.0,30.0,30.0,30.0,31.0,31.0,31.0,31.0,33.0,33.0,33.0,33.0,33.0,34.0,34.0,34.0,34.0,34.0,34.0,34.0,34.0,34.0,34.0,35.0,35.0,35.0,35.0，35.0,35.0,35.0， 35.0,36.0,36.0,36.0,37.0,37.0,37.0,38.0,38.0,38.0,38.0,39.0,39.0,39.0,39.0,39.0,39.0,39.0,39.0,39.0,39.0,40.0,40.0,49.0,40.0,40.0,40.0,41.0,41.0,41.0,41.0， 41.0,42.0,42.0,42.0,42.0,43.0,43.0,43.0,43.0,44.0,44.0,44.0,45.0,45.0,45.0,45.0,45.0,46.0,46.0,46.0,46.0,46.0,46.0,47.0,47.0， 47.0,47.0,47.0,49.0,49.0,49.0,49.0,49.0,50.0,50.0,51.0,51.0,51.0,51.0,51.0,52.0,52.0,52.0,52.0,52.0,53.0,52.0,52.0,53.0,53.0,53.0,53.0,54.0， 54.0,54.0,55.0,55.0,55.0,56.0,56.0,56.0,56.0,56.0,56.0,57.0,57.0,58.0,58.0,58.0,58.0,58.0,59.0,58.0,58.0,59.0,59.0,59.0,59.0,59.0,59.0,59.0,59.0,59.0,60.0,60.0， 60.0,60.0,60.0,60.0,60.0,61.0,61.0,61.0,61.0,61.0,61.0,61.0,61.0,62.0,61.0,62.0,62.0,63.0,63.0,62.0,63.0,63.0,63.0,64.0,64.0,63.0,64.0,64.0,64.0,64.0,64.0,64.0,64.0,64.0， 64.0, 64.0, 64.0, 65.0, 65.0, 65.0, 65.0, 65.0, 65.0, 66.0, 66.0, 66.0, 66.0, 66.0, 66.0, 67.0, 67.0 ，67.0,68.0,68.0,68.0,68.0,68.0,68.0,68.0,68.0,68.0,69.0,69.0,69.0,69.0,69.0,69.0,69.0,69.0,69.0,70.0,70.0,79.0,70.0,70.0,70.0,70.0,70.0,70.0,70.0,70.0,70.0,70.0,71.0,71.0 ，71.0,71.0,71.0,71.0,71.0,72.0,72.0,72.0,72.0,72.0,72.0,72.0,72.0,72.0,73.0,73.0,73.0,73.0,73.0,73.0,73.0,74.0,74.0,75.0,74.0,74.0,75.0,75.0,75.0,75.0,75.0,75.0,75.0,76.0 ，76.0,76.0,76.0,76.0,77.0,77.0,77.0,77.0,77.0,77.0,77.0,78.0,78.0,78.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,79.0,80.0,80,79.0,80.0,80.0 ，80.0,80.0,81.0,81.0,81.0,82.0,82.0,82.0,82.0,82.0,82.0,83.0,83.0,83.0,83.0,83.0,84.0,83.0,84.0,84.0,84.0,84.0,84.0,85.0,84.0,84.0,85.0,85.0,85.0,85.0,85.0,85.0,85.0,85.0 ，85.0,85.0,86.0,86.0,87.0,87.0,87.0,87.0,87.0,87.0,88.0,88.0,88.0,88.0,88.0,89.0,89.0,88.0,89.0,89.0,89.0,89.0,89.0,89.0,89.0,90.0,90.0,90.0,91.0,91.0,91.0 ，91.0,92.0,92.0,92.0,93.0,93.0,93.0,93.0,94.0,94.0,94.0,94.0,94.0,95.0,95.0,94.0,95.0,95.0,95.0,96.0,96.0,96.0,96.0,96.0,96.0,96.0,96.0,97.0,97.0,97.0,97.0,97.0,97.0,98.0 , 98.0, 98.0, 98.0, 99.0, 99.0, 99.0, 100.0, 100.0

空

我的输出：

平均值：47.21
中位数：47.00
方差：857.34 标准差：29.28

预期输出：

平均值：47.27
方差：856.71
标准差：29.27

BufferedReader stdin =
                    new BufferedReader (new InputStreamReader (System.in));
            NumberFormat nf = new DecimalFormat ("0.00");
            nf.setMinimumFractionDigits (2);//Sets Min digits
            nf.setMaximumFractionDigits (2);//Sets Max digits
            String inputValue;
            double sum = 0;
            double counter = 0;
            double median = 0;
            double variance = 0;
            double varianceCounter = 0;






            List<String> input = new ArrayList<String>();
            List<Double> numbers = new ArrayList<Double>();


            while((inputValue = stdin.readLine()) != null && !inputValue.equals("")){
                input.add(inputValue);
                numbers.add (Double.parseDouble(inputValue));        
            }
                 for(int i = 0; i < input.size(); i++){
                    sum += (numbers.get(i));
                    counter++;  
                }

            Collections.sort(numbers);
            for(int i = 0; i < numbers.size(); i++){
            if  (numbers.size() % 2 == 0){
                median = (numbers.get(numbers.size()/2-1) + numbers.get(numbers.size()/2))/2;
            }
            else {
                median = (numbers.get((numbers.size())/2));
            }
            }
            for(int i = 0; i < input.size(); i++){
                    variance += numbers.get(i) * numbers.get(i);
                    varianceCounter++;
            }






            System.out.println ("Mean: " + (nf.format(sum/counter)));
            System.out.println ("Median: " + (nf.format(median)));
            System.out.println ("Variance: " + (nf.format((variance/varianceCounter)-(sum*sum)/(varianceCounter*varianceCounter))));    
    System.out.println ("Standard Deviation: " + (nf.format(Math.sqrt((variance/varianceCounter)-(sum*sum)/(varianceCounter*varianceCounter)))));           
    }
    }

Answer 1

这就是在您的 IDE（如果不是您的调试器）中使用格式化程序有帮助的地方。

你遇到的问题是你对每个输入的所有值求和。

while ((inputValue = stdin.readLine()) != null && !inputValue.equals("")){
    input.add(inputValue);
    numbers.add (Double.parseDouble(inputValue));        
    // sum all the values on every input i.e. 1 1 2 1 2 3 1 2 3 4
    for (int i = 0; i < input.size(); i++){
        sum += (numbers.get(i));
        counter++;  
    }

您应该做的是读取所有输入，然后对所有值求和。

while ((inputValue = stdin.readLine()) != null && !inputValue.equals("")){
    input.add(inputValue);
    numbers.add (Double.parseDouble(inputValue));        
}
// sum all the values AFTER all the input. i.e. 1 2 3 4
for (int i = 0; i < input.size(); i++){
    sum += (numbers.get(i));
    counter++;  
}

顺便说一句，计数器应该始终是input.size()