主成分分析（PCA）の計算をする前にデータを標準化しないといけないらしい

#include <iostream>
#include <vector>
#include <array>

using vector3f = std::vector<std::array<float, 3>>;

//! @brief データの平均を求める
//! @param [in] vec データの配列
//! @return 各要素の平均
std::array<float, 3> Average(const vector3f& vec) {

  // 初期化
  std::array<float, 3> ave;
  ave[0] = 0;
  ave[1] = 0;
  ave[2] = 0;

  // 各要素平均
  for (size_t i = 0; i < vec.size(); i++) {
    ave[0] += vec[i][0];
    ave[1] += vec[i][1];
    ave[2] += vec[i][2];
  }
  ave[0] /= vec.size();
  ave[1] /= vec.size();
  ave[2] /= vec.size();

  return ave;

}

//分散
std::array<float, 3> Distributed(const std::array<float, 3>& average, const vector3f& vec) {
  int n = vec.size();
  std::array<float, 3> s2{ 0,0,0 };
  for (int j = 0; j < 3; j++) {
    for (const auto& v : vec) {
      s2[j] += std::pow(v[j] - average[j], 2);
    }
    s2[j] = 1.f / n * s2[j];
  }
  return s2;
}

//標準偏差
std::array<float, 3> StandardDeviation(const std::array<float, 3>& average, const vector3f& vec) {

  std::array<float, 3> d = Distributed(average, vec);
  d[0] = sqrt(d[0]);
  d[1] = sqrt(d[1]);
  d[2] = sqrt(d[2]);

  return d;
}

//標準化　平均を引いて標準偏差で割る
// average 平均
// sd 標準偏差
void Standardization(vector3f& src, const std::array<float, 3>& average, const std::array<float, 3>& sd) {
  for (auto&& p : src) {
    p[0] = (p[0] - average[0]) / sd[0];
    p[1] = (p[1] - average[1]) / sd[1];
    p[2] = (p[2] - average[2]) / sd[2];
  }
}

int main()
{
  vector3f data;

  data.push_back({ -1.841658711,0.324050009,1.041258931 });
  data.push_back({-1.449076772,0.431593835,0.987673104 });
  data.push_back({-1.04681015,0.415599823,1.049820662 });
  data.push_back({-0.646572888,0.42549479,1.087714672 });
  data.push_back({-0.25920701,0.599574149,0.971796691 });
  data.push_back({ 0.149769783,0.497985959,1.114130974 });
  data.push_back({-1.883069754,0.6849733,1.249212146 });
  data.push_back({-1.481496215,0.677821219,1.303076267 });
  data.push_back({-1.083532453,0.716715276,1.313803315 });


  std::array<float, 3> _s = Average(data);
  std::array<float, 3> sd = StandardDeviation(_s, data);

  Standardization(data, _s, sd);

  for (size_t i = 0; i < data.size(); i++) {
    printf("%lf , %lf , %lf\n", data[i][0], data[i][1], data[i][2]);
  }

}