接收0嘗試計算標準偏差

Question

我在哪裏我試圖計算標準偏差的問題，但我只是結束了0

值的代碼如下，但問題發生在這些線路上：

int sizeofthis = intervalsForMath.size(); 
    Log.d("sizeofThis", "" + sizeofthis); 
    double averageDistFromMean = sum/sizeofthis; 

我使用整數或浮點數，而不是嘗試，但我仍然得到的結果爲零，當它應該是在0.5左右。

我將粘貼下面的logcat的輸出，如果沒有什麼幫助。

有沒有人有任何想法？

public ArrayList<Integer> DoMathStdDev(ArrayList<Integer> intervalsForMath) { 


    ArrayList<Integer> timeDataCalc = new ArrayList<Integer>(); // Array to contain the recently calculated bpms and delay times    

    timeDataCalc.add(0, (intervalsForMath.get(intervalsForMath.size() - 1))); // Get Last Interval 
    ArrayList <Integer> sanitisedIntervalsForMath = new ArrayList<Integer>(); //Create Array to hold array with unusual entries removed 
    if (intervalsForMath.size() >= 4) { //Only want to get standard deviation if the array has 4 values or more 
    int sum = 0; //reset sum 
    for (int ii = 0; ii < intervalsForMath.size(); ii++) { 
     sum = sum + (intervalsForMath.get(ii)); //create total of all the entries as sum 
    } 
    int average = (sum/(intervalsForMath.size())); //take average from the total (sum) divided by intervals size 
    Log.d("average", "" + average); //I'll put the results of the log at the bottom 

    // calculate distance from mean of all indices 
    ArrayList<Integer> distFromMean = new ArrayList<Integer>(); //Create arraylist for DistFrom Mean 
    for (int i = 0; i < intervalsForMath.size(); i++) { 
     distFromMean.add(i, (intervalsForMath.get(i)-average)); //Create DistFromMean, distance from average for each entry 
    } 
    Log.d("distFromMean", "" + distFromMean); 

    sum = 0; //reset sum 
    for (int iii = 0; iii < distFromMean.size(); iii++) { 
     sum = sum + (distFromMean.get(iii)); //create total of all the entries as sum 
    } 
    Log.d("sum", "" + sum); 
    Log.d("intervalsForMath.size", "" + intervalsForMath.size()); 
    int sizeofthis = intervalsForMath.size(); 
    Log.d("sizeofThis", "" + sizeofthis); 
    double averageDistFromMean = sum/sizeofthis; 
    Log.d("averageDistFromMean", "" + averageDistFromMean); 
    double stdDeviation = sigma*(Math.sqrt(averageDistFromMean)); //take average from that and square root it for StdDev and times it by the sigma amount 
    Log.d("sigma", "" + sigma); 
    Log.d("stdDeviation", "" + stdDeviation); 


     // I THINK YOU CAN IGNORE EVERYTHING BELOW HERE 


    //remove intervals that fall outside the standard deviation 

    for (int iiii = 0; iiii < intervalsForMath.size(); iiii++) { //For each index in intervals for Math 
     if (intervalsForMath.get(iiii) <= (average+stdDeviation) || intervalsForMath.get(iiii) >= (average-stdDeviation)) { // Check if the entry is inside the standard deviation 
      sanitisedIntervalsForMath.add(intervalsForMath.get(iiii)); //Add entries that pass that check into the sanitisedIntervalsForMath array 
     }  
    } 

    } else { 
     for (int iiiii = 0; iiiii < intervalsForMath.size(); iiiii++) { 
      sanitisedIntervalsForMath.add(iiiii, intervalsForMath.get(iiiii)); 
     } 
    } 

    int numberOfIndices; 
    if (sanitisedIntervalsForMath.size() <= 3) { 
     numberOfIndices = sanitisedIntervalsForMath.size(); 
    } else { 
     numberOfIndices = 4; 
    } 

    if (numberOfIndices == 1) { 

     timeDataCalc.add(1, 
       (sanitisedIntervalsForMath.get(intervalsForMath.size() - 1))); 
     timeDataCalc.add(2, 
       (sanitisedIntervalsForMath.get(intervalsForMath.size() - 1))); 
     timeDataCalc.add(3, 
       (sanitisedIntervalsForMath.get(intervalsForMath.size() - 1))); 
     timeDataCalc.add(4, 
       (sanitisedIntervalsForMath.get(intervalsForMath.size() - 1))); 

    } else { 
     // Get last 4 intervals represented as WXYZ 

     ArrayList<Integer> intervalsWXYZ = new ArrayList<Integer>(); 
     for (int i = (sanitisedIntervalsForMath.size()) - numberOfIndices; i < sanitisedIntervalsForMath 
       .size(); i++) { 
      intervalsWXYZ.add(sanitisedIntervalsForMath.get(i)); 
     } 

     // Get last4BeatsMedian, add it to timeDataCalc index 1 
     Collections.sort(intervalsWXYZ); 
     if ((intervalsWXYZ.size() % 2) == 0) { 
      timeDataCalc.add(1,((intervalsWXYZ.get((int) ((intervalsWXYZ.size()/(float) 2) - 1))) + (intervalsWXYZ.get((int) ((intervalsWXYZ.size()/((float) 2)) + 0))))/2); 
     } else { 
      timeDataCalc.add(1, (intervalsWXYZ.get((int) (intervalsWXYZ.size()/(float) 2)))); 
     } 
     // Get last4BeatsMean, add it to timeDataCalc index 2 
     int sum = 0; 
     for (int i = 0; i < intervalsWXYZ.size(); i++) { 
      sum = sum + (intervalsWXYZ.get(i)); 
     } 
     timeDataCalc.add(2, (sum/(intervalsWXYZ.size()))); 
     intervalsWXYZ.clear(); 

     // Get Whole Session Median & Mean 

     if (intervalsForMath.size() >= 4) { 

      // Get Whole Session Median, add it to timeDataCalc index 3 

      ArrayList<Integer> intervalsWhole = new ArrayList<Integer>(); 
      for (int i = 0; i < sanitisedIntervalsForMath.size(); i++) { 
       intervalsWhole.add(sanitisedIntervalsForMath.get(i)); 
      } 
      Collections.sort(intervalsWhole); 
      if ((intervalsWhole.size() % 2) == 0) { 
       timeDataCalc 
         .add(3, 
           ((intervalsWhole.get((int) ((intervalsWhole 
             .size()/(float) 2) - 1))) + (intervalsWhole 
             .get((int) ((intervalsWhole.size()/((float) 2)) + 0))))/2); 
      } else { 
       timeDataCalc.add(3, (intervalsWhole 
         .get((int) (intervalsWhole.size()/(float) 2)))); 
      } 

      // Get Whole Session Mean, add it to timeDataCalc index 4 
      sum = 0; //reset sum 
      for (int ii = 0; ii < intervalsWhole.size(); ii++) { 
       sum = sum + (intervalsWhole.get(ii)); //create total of all the entries as sum 
      } 
      int average = (sum/(intervalsWhole.size())); //take average from that 
      timeDataCalc.add(4, average); 
      intervalsWhole.clear(); 
     } 
    } 


    return timeDataCalc; 
} 

logcat的輸出：

平均：264

distFromMean：[-264,224,28,17，-50，-78，-42，-94，-89，-94， - 76，-105，-107,39，-96，-90，-92，-413，-107，-88，-114，-93，-100，-92,32，-127，-125，-93 ，1478]

總和：15

intervalsForMath.size：29

個

sizeofThis：29

averageDistFromMean：0.0

西格瑪：1.0

stdDeviation：0.0

Answer 1

您正在執行整數除法，這將經常返回（有點）意外的結果。

當計算兩個整數的，結果被計算爲的整數，然後轉換爲一個雙。因此你失去了你需要的精確度。

鑄造你的整數中的一個（或兩個）的雙像這樣會產生你你所期望的。

double averageDistFromMean = sum/(double)sizeofthis;