我遇到了一个问题，我试图计算标准差，但最终得到的值为 0。
代码如下，但问题出现在这些行上:
int sizeofthis = intervalsForMath.size();
Log.d("sizeofThis", "" + sizeofthis);
double averageDistFromMean = sum/sizeofthis;
我尝试使用 int 或 float 代替，但结果仍然为零，而它应该在 0.5 左右。
我将在下面粘贴 LogCat 输出，以防有帮助。
有人有什么想法吗？
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 输出:
平均:264
距离平均值:[-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]
总和:15
intervalsForMath.size:29
大小:29
平均距离:0.0
西格玛:1.0
标准偏差:0.0
最佳答案
您正在执行整数除法，这通常会返回(有些)意外的结果。
当您除两个整数时，结果将计算为整数，然后转换为 double 型。因此，您失去了所需的精度。
像这样将一个(或两个)整数转换为 double 将产生您所期望的结果。
double averageDistFromMean = sum / (double)sizeofthis;
关于java - 尝试计算标准差时收到 0，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19282235/