使用C++实现Excel中的stdev.p函数

使用C++实现Excel中的stdev.p函数，用来计算标准差。Excel计算示例如下：周期为5。

使用自定义的C++函数计算，运行结果如下：

完整的可运行代码如下：

#include <iostream>

#include <cstdio>

#include <vector>

using namespace std;

//标准差计算函数

double StdEvP(std::vector<double>& vc, int nPeriod)

{

?????? if (nPeriod <= 0) { return 0; }

?????? int sz = (int)vc.size();

?????? if (sz < nPeriod) { return std::nan(""); }

?????? int i = 0, nBegin = sz - nPeriod;

?????? // 计算均值

?????? double dbAvg = 0;

?????? for (i = sz - 1; i >= nBegin; --i)

?????? {

????????????? dbAvg += vc[i];

?????? }

?????? dbAvg /= nPeriod;

?????? // 计算方差的和

?????? double dbStdDev = 0;

?????? for (i = sz - 1; i >= nBegin; --i)

?????? {

????????????? dbStdDev += pow((vc[i] - dbAvg), 2);

?????? }

?????? // 计算平均方差

?????? dbStdDev /= nPeriod;

?????? // 计算标准差

?????? dbStdDev = sqrt(dbStdDev);

?????? return dbStdDev;

}

//测试程序

int main()

{

?????? int num[] = { 1,2,3,4,5,6,7,8,9,10,10,10,11,10,10,9,8,7,6,5,4,3,2,1,1,5,6,7,8,9 };

?????? std::vector<double> vcTmp;

?????? std::vector<double> vcStd;

?????? for (int i = 0; i < sizeof(num) / sizeof(int); ++i)

?????? {

????????????? vcTmp.push_back(num[i]);

????????????? double stdevp = StdEvP(vcTmp, 5);

????????????? vcStd.push_back(stdevp);

?????? }

?????? for (size_t i = 0; i < vcTmp.size(); ++i)

?????? {

????????????? if (isnan(vcStd[i]))

????????????? {

???????????????????? printf("%-6d\n", num[i]);

????????????? }

????????????? else

????????????? {

???????????????????? printf("%-6d %.3lf\n", num[i], vcStd[i]);

????????????? }

?????????????

?????? }

?????? return 0;

}