docs: def fit_df(self, labels, dfs, pstate_col=PSTATE_COL):
          """
          Fit the classifier with labels y and DataFrames dfs
          """
          assert len(labels) == len(dfs)
  
          for label in set(labels):
              label_dfs = [s for l,s in zip(labels, dfs) if l == label]
  
              pohmm = self.pohmm_factory()
              pohmm.fit_df(label_dfs, pstate_col=pstate_col)
              self.pohmms[label] = pohmm
  
          return self