code: def split(expr, frac, seed=None):
      
      if hasattr(expr, '_xflow_split'):
          return expr._xflow_split(frac, seed=seed)
      else:
          return _split(expr, frac, seed=seed)
docs: Split the current column into two column objects with certain ratio.
  
      :param float frac: Split ratio
  
      :return: two split DataFrame objects