code: def _build_stat(self, idx):
          
          nameordered = self.samples.keys()
          nameordered.sort()
          newdat = pd.DataFrame([self.samples[i].stats_dfs[idx] \
                                 for i in nameordered], index=nameordered)\
                                 .dropna(axis=1, how='all')
          return newdat
docs: Returns a data frame with Sample stats for each step