code: def toColumns(self):
      return (
          self.string_cols1
          + self.int_cols1
          + self.string_cols2
          + self.int_cols2
          + self.bool_cols1
          + self.int_cols3
          + self.string_cols3
          + self.int_cols4
          + self.bool_cols2
          + self.int_cols5
          + self.bool_cols3
          + self.float_cols
      )
  
file_path: BigDL/python/friesian/example/wnd/recsys2021/valid_to_parquet.py
imports: import os
  from time import time
  from argparse import ArgumentParser
  from bigdl.orca import init_orca_context, stop_orca_context
  from bigdl.friesian.feature import FeatureTable
  from bigdl.dllib.utils.log4Error import *
label_desc: Use image node_id 2 for calling the RecsysSchema obj's underlying member method code with example usage: obj.toColumns() and returns: unknown