code: def sample_group(sid, groups):
      
      for name in groups:
          if sid in groups[name].sids:
              return name
docs: Iterate through all categories in an OrderedDict and return category name if SampleID
      present in that category.
  
      :type sid: str
      :param sid: SampleID from dataset.
  
      :type groups: OrderedDict
      :param groups: Returned dict from phylotoast.util.gather_categories() function.
  
      :return type: str
      :return: Category name used to classify `sid`.