java - 统计计算器 - 中位数问题和标准差 java

Question

我正在开发一个统计计算器...仍然...我仍然遇到一些问题..我已经解决了大部分问题，但是，我仍然遇到问题..中位数排序但没有'实际上计算中位数是多少。另外，老实说我不知道​​如何在 java 中进行标准偏差。是的，我知道它是方差的平方根，但我不知道如何计算方差或如何实际将数学方程放入java中。在这方面我得到了一位 friend 的很多帮助。不幸的是，我患有短期内存丧失，我很容易忘记事情，仍然没有借口，但我正在寻求一些帮助。 Java 确实让我大吃一惊，我知道这是很容易的事情，而且会变得更难，但我正在努力学习。

    import java.util.Scanner; // Scanner is in the java.util package

public class BasicStatisticsCalculator 
{   
    static final int NUMBER_OF_ELEMENTS=6;
    static int[] numbers=new int[NUMBER_OF_ELEMENTS];



    public static void main(String[] args) 
    {

       do
            {   
                switch(menu())
                {
                   case 'a': insertSeries(numbers); break;
                   case 'b': mean(numbers); break;
                   case 'c': median(numbers); break;
                   case 'd': mode(numbers); break;
                   case 'e': sd(numbers); break;                   

                   case 'f': showSeries(numbers); break;
                   case 'g': greaterThanMean(numbers); break;
                   case 'h': smallerThanMean(numbers); break;                      
                   case 'i': bubbleSort(numbers); break;
                   case 'j': fullReport(numbers); break;

                   case 'q': System.exit(0);
                } 
            }
           while(true);
    }

    //Menu Display
    static char menu(){
       Scanner input=new Scanner(System.in);

       System.out.println("\n\nBASIC STATISTICS CALCULATOR");
       System.out.println(" a. Insert Series");
       System.out.println(" b. Mean");
       System.out.println(" c. Median");
       System.out.println(" d. Mode"); 
       System.out.println(" e. Standard Deviation");       

       System.out.println(" f. Show Series");
       System.out.println(" g. Show Elements greater than the mean");
       System.out.println(" h. Show Elements smaller than the mean");
       System.out.println(" i. Show series in order");
       System.out.println(" j. Show Full Report");   

       System.out.println("\n q. Quit");
       System.out.print("\nInsert option: "); 

       return(input.next().charAt(0));  
    }//END menu display   

    /*Insert series */
    static void insertSeries(int[] numbers)
        {
            java.util.Scanner input = new java.util.Scanner(System.in);
            for (int i = 0; i < numbers.length; i++) 
            {
              System.out.print("Enter a new number: ");
              numbers[i] = input.nextInt();
            }
        }//END USER INPUT PROMPT 


    /*Show series */
    static void showSeries(int[] numbers)
        {
            System.out.print("\nSeries: ");
            for (int i = 0; i < numbers.length; i++) 
            {
              System.out.print(numbers[i]+" ");
            }
        }//END DISPLAY SERIES

    /*Show series overloaded with two parameters */
    static void showSeries(int[] numbers, String s)
        {
            System.out.print("\n"+s);
            for (int i = 0; i < numbers.length; i++) 
            {
              System.out.print(numbers[i]+" ");
            }
        }          


    /*Find the mean value */
    static void mean(int[] numbers)
        {
            float sum=0;
            for (int i = 0; i < numbers.length; i++) sum+=numbers[i];  
            System.out.print("\nMean: "+sum/numbers.length);        
        }//END MEAN   

        static float mean2(int[] numbers)
        {
            float sum=0;
            for (int i = 0; i < numbers.length; i++) sum+=numbers[i];  
            return (sum/numbers.length);        
        } 

    /*Find the median value */
    public static double median(int[] numbers)
        {
               int[] numbers2=bubbleSort(numbers);
            for (int i = 0; i < numbers.length; i++);

                int indexB = numbers.length / 2;
                int indexA = (numbers.length - 1) / 2;
            double median;
            if (numbers.length % 2 == 0)


            median = ((double)(numbers[numbers.length/2] + (double)numbers[numbers.length/2 - 1]))/2;
            else 
            median = ((double) (numbers2[indexA] + numbers2[indexB])) / 2;

                System.out.println("\nThe median number is : " + median);
            return 0;

        }//END MEDIAN



    /*Find the mode value */
    static void mode(int[] numbers)
        {
            //Create a frequency vector
            int offset=min(numbers);
            int[] numbers2=numbers.clone();
            for(int i=0; i<numbers2.length; i++) numbers2[i]=numbers[i]-offset;     

            int interval=max(numbers)-offset;
            int[] frequency=new int[interval+1];
            for(int i=0; i<numbers.length; i++) frequency[numbers2[i]]++;

            if (maxIndex(frequency)==-1) System.out.print("\nMode: All elements have the same frequency");
            else System.out.print("\nMode: "+((maxIndex(frequency))+offset));
        }//End Mode   


    /*Find the maximum value */
    static int max(int[] numbers)
        {
        int max=numbers[0];
        for (int i = 1; i < numbers.length; i++) if(max<numbers[i]) max=numbers[i];              
        return max;        
        }//End Max Value  

    /*Find the minimum value */
    static int min(int[] numbers)
        {
            int min=numbers[0];
            for (int i = 1; i < numbers.length; i++) if(min>numbers[i]) min=numbers[i];
            return min;        
        }  

    /*Find the maximum value */
    static int maxIndex(int[] frequency)
        {
        boolean noMax=true;
        //Check to see if there is no maximum
        int max=max(frequency);
        for (int i = 0; i < frequency.length; i++) if (max!=frequency[i] && frequency[i]!=0) noMax=false;

        //Return the index associated to the maximum
        if(noMax) return -1;
        else
                {
                    max=frequency[0];
                    int index=0;
                    for (int i = 0; i < frequency.length; i++) if(max<frequency[i]) {max=frequency[i]; index=i;}
                    return index;
        }//End else
        }//End MAX Value  index 


    /*Find the standard deviation */
    /*Find the standard deviation */
    static void sd(int[] numbers){


         //Standard deviation
         double x = 0;
         double average = mean2(numbers);

         //Subtract mean from each number and square it
         for (int i = 0; i < numbers.length; i++)  x = x +((numbers[i] - average)*(numbers[i] - average));

         //find mean
         x = x  / (numbers.length-1);

         //square root
         double sd = Math.sqrt(x);

         //Show Standard deviation
         System.out.print("\nStandard deviation: "+ sd);

    }     

    /*Show values greater than mean */
    static void greaterThanMean(int[] numbers)
        {
            float sum=0;
            float mean;
            for (int i = 0; i < numbers.length; i++) sum+=numbers[i]; 
            mean=sum/numbers.length;

            System.out.print("\nElements greater than mean: ");  
            for (int i = 0; i < numbers.length; i++) if (numbers[i]>mean) System.out.print(numbers[i]+" ");    
        }  

    /*Show values smaller than mean */
    static void smallerThanMean(int[] numbers)
        {
            float sum=0;
            float mean;
            for (int i = 0; i < numbers.length; i++) sum+=numbers[i]; 
            mean=sum/numbers.length;

            System.out.print("\nElements smaller than mean: ");  
            for (int i = 0; i < numbers.length; i++) if (numbers[i]<mean) System.out.print(numbers[i]+" ");    
        }  


    /*Bubble sort algorithm */
        public static int[] bubbleSort(int[] series)
        {
      if (series!=null) 
            {
            int[] vector=series.clone();

            int aux;
            for (int i=0; i<vector.length; i++)
                        {
                   for(int j=0; j<vector.length-(i+1); j++)
                                   {
                            if(vector[j]>vector[j+1])
                                                        {
                                aux=vector[j+1];
                                vector[j+1]=vector[j];
                                vector[j]=aux;
                            }
                                    }
            }   
            showSeries(vector,"Ordered series: ");
            }
        return numbers; 
    }//END SORT 


    /*Show all statistics*/
    static void fullReport(int[] numbers)
        {
           showSeries(numbers);
           mean(numbers);
           median(numbers);
           mode(numbers);
           sd(numbers);
           greaterThanMean(numbers);
           smallerThanMean(numbers);
           bubbleSort(numbers);          
        } 

}//End BasicStatisticCalculator

Answer 1

虽然以下内容未经测试，但它们应该可以工作。对于中位数:

public static double median(int[] numbers) {
      Arrays.sort(numbers); // sort numbers
      int len = numbers.length;

      if (len % 2 == 0) // length is even
          return (numbers[len/2] + numbers[len/2-1]) / 2.0d;

      else // length is odd
          return (double) numbers[len/2];

}

标准差是数字与平均值的平均距离，因此首先计算数字集的平均值(您已经有一个函数)。然后做这样的事情:

static double sd(int[] numbers) {

    double mean = mean(numbers);
    double std_dev = 0;

    for (int i=0; i<numbers.length; i++) {
        std_dev += Math.pow(mean - (double) numbers[i], 2);
    }

    // This gets the population standard deviation 
    return Math.sqrt(std_dev / (double) (numbers.length-1) );


}  

有关总体标准差的更多信息，请参见此处:Population Standard Deviation