text: #ifndef _preprocessing_hpp_
  #define _preprocessing_hpp_
  
  #include <all.hpp>
  
  class Preprocessing {
    private:
      bool if_mean = false, if_std = false;
      Matrix mean, std;
  
    public:
      Matrix normalize(Matrix, std::string);
      ~Preprocessing() {}
  };
  
  // Method to normalize the dataset
  Matrix Preprocessing::normalize(Matrix mat, std::string dim) {
      if (!if_mean) {
          mean = matrix.mean(mat, dim);
          if_mean = true;
      }
      if (!if_std) {
          std = matrix.std(mat, dim);
          if_std = true;
      }
      Matrix result = (mat - mean) / std;
      return result;
  }
  
  #endif /* _preprocessing_h_ */
  