class_docstr: Todo:
  check treatment of const, make it optional ?
      add hasconst (0 or 1), needed when selecting nfact+hasconst
  options are arguments in calc_factors, should be more public instead
  cross-validation is slow for large number of observations
code: def __init__(self, endog, exog):
      # do this in a superclass?
      self.endog = np.asarray(endog)
      self.exog = np.asarray(exog)
  
file_path: statsmodels/statsmodels/sandbox/datarich/factormodels.py
imports: import numpy
  import statsmodels.api
  from statsmodels.sandbox.tools import pca
  from statsmodels.sandbox.tools.cross_val import LeaveOneOut
label_desc: Use image node_id 1 to create a new FactorModelUnivariate object  with example: obj = FactorModelUnivariate(endog, exog)