如何计算一个数组的平均值[] []

Question

我计算了两个数组的长度总和，以获得平均值。我现在想要做的是计算数组内的数字总和，以便我可以计算标准偏差。

jbtnGenerate.addActionListener(new ActionListener() { 
    public void actionPerformed(ActionEvent ae) { 
     try { 
      // variable for the sum 
      double sum = 0; 
      // variable for standard deviation 
      double ecartTypeXbarre = 0; 
      // variable to calculate the numbers but squared 
      double sommeXcarre = 0; 
      double ecartType1 = 0; 
      double moyenneXbarre = 0;// that's the average 
      int lengths = 0; 
      // Variable for Size of Samples 
      int tailleEchantillon = Integer.parseInt(jtfn.getText()); 
      // Variable to get number of samples 
      int nombreEchantillon = Integer.parseInt(jtfNbEchantillons.getText()); 

      // Variable where i stock both previous ones 
      double echantillon[][] = new double[tailleEchantillon][nombreEchantillon]; 

      // Generates random numbers taken from data which is an ArrayList of 
      // doubles and puts it into echantillon 
      for (int i = 0; i < tailleEchantillon; i++) { 
       for (int j = 0; j < nombreEchantillon; j++) 
        echantillon[i][j] = data.get(rng.nextInt(data.size())); 
      } 

      // puts the numbers into a TextArea 
      for (int i = 0; i < tailleEchantillon; i++) { 
       for (int j = 0; j < nombreEchantillon; j++) 
        jta.append(String.valueOf(echantillon[i][j]) + "\n"); 
      } 
       //Calculating avg and sum 
      for (int i = 0; i < echantillon.length; i++) { 
        //Calculates the lengths of the first array 
        lengths += echantillon[i].length; 
//sommeXbarre is supposed to be the sum of values inside echantillon 
        sommeXbarre+= lengths; 

        double xCarre1 = lengths * lengths; 

        sommeXcarre += xCarre1; 

        //Calculates the average += echantillon 
        for (int k = 0; k < echantillon[i].length; k++) { 

         moyenneXbarre += echantillon[i][k]; 
        } 
       } 
            //That's where my average is calculated 
       moyenneXbarre /= lengths; 
      //Trying to calculated the standard deviation 
// Inside this ((sommeXbarre * sommeXbarre) I need the sum of numbers which Im not able to get 

      ecartType1 = Math.sqrt(
       (sommeXcarre - ((sommeXbarre * sommeXbarre)/echantillon.length)) 
       /echantillon.length 
      ); 

      ecartTypeXbarre = ecartType1/Math.sqrt(tailleEchantillon); 

      jtfMoyenneXBarre.setText(String.valueOf(moyenneXbarre)); 
      jtfEcartTypeXBarre.setText(String.valueOf(ecartTypeXbarre)); 
     } 
     catch (NumberFormatException e) { 

     } 
    } 
}); 

Answer 1

如果子阵列都是一样的大小，如果你宣布一个int[][] ray = new int[2][2];可以或多或少地做到这一点：

int[][] ray = { { 1, 2 }, { 3, 4 } }; 

// ray.length == 2 
// ray[0].length == 2 
// ray[1].length == 2 

double avg = 0; 

for (int i = 0; i < ray.length; i++) { 
    for (int k = 0; k < ray[i].length; k++) { 
     avg += ray[i][k]; 
    } 
} 

avg /= ray.length * ray[0].length; 

的问题是在Java中，他们不必是。你可以这样做：

int[][] ray = { { 1 }, { 2, 3, 4 } }; 

// ray.length == 2 
// ray[0].length == 1 
// ray[1].length == 3 

那么你真的应该总结的长度也：

double avg = 0; 
int lengths = 0; 

// loop for ray.length 
// ray.length == number of arrays in ray 
for (int i = 0; i < ray.length; i++) { 
    lengths += ray[i].length; 

    // loop for ray[i].length 
    // ray[i].length == number of elements in ray[i] 
    for (int k = 0; k < ray[i].length; k++) { 
     avg += ray[i][k]; 
    } 
} 

avg /= lengths;