code: def common_items_metrics(all_items, common_items):
      
      segments = common_items.index.unique()
      metrics = {}
      for seg in segments:
          seg_common_items = segment_common_items(seg)
          projects = get_segment_projects(seg)
  
          metric_values = []
  
          for proj in projects:
              pronac = proj[0]
              percentage = common_items_percentage(pronac, seg_common_items)
              metric_values.append(percentage)
  
          metrics[seg] = {
              'mean': np.mean(metric_values),
              'std': np.std(metric_values)
          }
      return pd.DataFrame.from_dict(metrics, orient='index')
docs: Calculates the percentage of common items for each project
      in each segment and calculates the mean and std of this percentage
      for each segment.