code: def subset(self, *args):
          
          df = self._subset(*args)
          if df is None:
              self.err("Can get subset of data")
              return
          self.df = df
docs: Set the main dataframe to a subset based in positions
          Select a subset of the main dataframe based on position:
          ex: ds.subset(0,10) or ds.subset(10) is equivalent: it starts
          at the first row if only one argument is provided