Currently our implementation of set_index only supports columns labels, but the actual implementation also allows passing Index or Series instances. `df.set_index([df.index, df.foo, df['baz']])` Imported from Jira [BEAM-11711](https://issues.apache.org/jira/browse/BEAM-11711). Original Jira may contain additional context. Reported by: bhulette.