code: def split_(self, col: str) -> "list(Ds)":
          
          try:
              dss = {}
              unique = self.df[col].unique()
              for key in unique:
                  df2 = self.df.loc[self.df[col] == key]
                  ds2 = self._duplicate_(df2)
                  dss[key] = ds2
              return dss
          except Exception as e:
              self.err(e, "Can not split dataframe")
docs: Split the main dataframe according to a column's unique values and
          return a dict of dataswim instances
  
          :return: list of dataswim instances
          :rtype: list(Ds)
  
          :example: ``dss = ds.slit_("Col 1")``