code: def build_columns(self, X, verbose=False):
          
          return sp.sparse.csc_matrix(X[:, self.feature][:, np.newaxis])
docs: construct the model matrix columns for the term
  
          Parameters
          ----------
          X : array-like
              Input dataset with n rows
  
          verbose : bool
              whether to show warnings
  
          Returns
          -------
          scipy sparse array with n rows