def sample_group(sid, groups):
for name in groups:<EOL><INDENT>if sid in groups[name].sids:<EOL><INDENT>return name<EOL><DEDENT><DEDENT>
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`.