pydata/pandas — pull request #6356 by jreback (2014-02-14 16:42:40+00:00)
Title: ENH/BUG: allow single versus multi-index joining on inferred level (GH3662)

WIP on #3662

```
In [4]: household.join(portfolio, how='inner')
Out[4]:
male wealth name share
household_id asset_id
1 nl0000301109 0 196087.3 ABN Amro 1.00
2 nl0000289783 1 316478.7 Robeco 0.40
gb00b03mlx29 1 316478.7 Royal Dutch Shell 0.60
3 gb00b03mlx29 0 294750.0 Royal Dutch Shell 0.15
lu0197800237 0 294750.0 AAB Eastern Europe Equity Fund 0.60
nl0000289965 0 294750.0 Postbank BioTech Fonds 0.25

[6 rows x 4 columns]

In [5]: household.join(portfolio, how='outer')
Out[5]:
male wealth name share
household_id asset_id
1 nl0000301109 0 196087.3 ABN Amro 1.00
2 nl0000289783 1 316478.7 Robeco 0.40
gb00b03mlx29 1 316478.7 Royal Dutch Shell 0.60
3 gb00b03mlx29 0 294750.0 Royal Dutch Shell 0.15
lu0197800237 0 294750.0 AAB Eastern Europe Equity Fund 0.60
nl0000289965 0 294750.0 Postbank BioTech Fonds 0.25
4 NaN NaN NaN NaN 1.00

[7 rows x 4 columns]

In [8]: household.index.name='foo'

In [9]: household.join(portfolio, how='outer')

ValueError: cannot join with no level specified and no overlapping names
```