pydata/pandas — pull request #6639 by jreback (2014-03-14 21:38:21+00:00)
Title: API: A tuple passed to DataFame.sort_index will be interpreted as the levels of the index (GH4370)

closes #4370

```
In [3]: df = DataFrame({'one':[2,1,1,1],'two':[1,3,2,4],'three':[5,4,3,2]})

In [7]: df.columns = MultiIndex.from_tuples([('a','one'),('a','two'),('b','three')])

In [8]: df
Out[8]:
a b
one two three
0 2 5 1
1 1 4 3
2 1 3 2
3 1 2 4

[4 rows x 3 columns]
```

These are now equivalent. Used to be able to do only the 2nd.

```
In [9]: df.sort_index(by=('a','two'))
Out[9]:
a b
one two three
3 1 2 4
2 1 3 2
1 1 4 3
0 2 5 1

[4 rows x 3 columns]

In [10]: df.sort_index(by=[('a','two')])
Out[10]:
a b
one two three
3 1 2 4
2 1 3 2
1 1 4 3
0 2 5 1

[4 rows x 3 columns]
```