panel ix change in 0.8?
seems p.ix[:,[-1],:] throws an exception (from take)
p.ix[:,-1:,:] is the workaround
maybe add to the docs?

ipython session follows:
9/10/12 panel test ix change

```
1/2
In [7]:
In [2]:
Out[2]: <class 'pandas.core.panel.Panel'>
Dimensions: 2 (items) x 8 (major) x 4 (minor)
Items: Item1 to Item2
Major axis: 2000-01-01 00:00:00 to 2000-01-08 00:00:00
Minor axis: A to D
In [6]:
\---------------------------------------------------------------------------
Exception Traceback (most recent call last)
/mnt/home/jreback/<ipython-input-6-1531bef93beb> in <module>()
1 # this worked prior to 0.8
----> 2 p.ix[:,[-1],:]
/usr/local/lib/python2.7/site-packages/pandas-0.8.1-py2.7-linuxx86_
64.egg/pandas/core/indexing.pyc in __getitem__(self, key)
31 pass
32
---> 33 return self._getitem_tuple(key)
34 else:
35 return self._getitem_axis(key, axis=0)
/usr/local/lib/python2.7/site-packages/pandas-0.8.1-py2.7-linuxx86_
64.egg/pandas/core/indexing.pyc in _getitem_tuple(self, tup)
137 continue
138
--> 139 retval = retval.ix._getitem_axis(key, axis=i)
140
141 return retval
/usr/local/lib/python2.7/site-packages/pandas-0.8.1-py2.7-linuxx86_
64.egg/pandas/core/indexing.pyc in _getitem_axis(self, key, axis)
247 raise ValueError('Cannot index with multidimensional key')
248
--> 249 return self._getitem_iterable(key, axis=axis)
250 elif axis == 0:
251 is_int_index = _is_integer_index(labels)
/usr/local/lib/python2.7/site-packages/pandas-0.8.1-py2.7-linuxx86_
64.egg/pandas/core/indexing.pyc in _getitem_iterable(self, key, axis)
295
296 if _is_integer_dtype(keyarr) and not _is_integer_index(labels):
--> 297 return self.obj.take(keyarr, axis=axis)
298
299 # this is not the most robust, but...
/usr/local/lib/python2.7/site-packages/pandas-0.8.1-py2.7-linuxx86_
64.egg/pandas/core/generic.pyc in take(self, indices, axis)
857 new_data = self._data.reindex_axis(new_items, axis=0)
858 else:
import pandas
index = pandas.date_range('1/1/2000', periods=8,)
p = pandas.Panel(np.random.randn(2, len(index), 4), items=['Item1', 'Item2'], major_axis
p

\# this worked prior to 0.8
p.ix[:,[-1],:]
9/10/12 panel test ix change
2/2
--> 859 new_data = self._data.take(indices, axis=axis)
860 return self._constructor(new_data)
861
/usr/local/lib/python2.7/site-packages/pandas-0.8.1-py2.7-linuxx86_
64.egg/pandas/core/internals.pyc in take(self, indexer, axis)
1075 n = len(self.axes[axis])
1076 if ((indexer == -1) | (indexer >= n)).any():
-> 1077 raise Exception('Indices must be nonzero and less than '
1078 'the axis length')
1079
Exception: Indices must be nonzero and less than the axis length
In [5]:
Out[5]: <class 'pandas.core.panel.Panel'>
Dimensions: 2 (items) x 1 (major) x 4 (minor)
Items: Item1 to Item2
Major axis: 2000-01-08 00:00:00 to 2000-01-08 00:00:00
Minor axis: A to D
In [ ]:

\# this works ok
p.ix[:,-1:,:]
```
