Obtengo un KeyError cuando intento trazar una porción de una columna de DataFrame de pandas con tiempos de datos en ella. ¿Alguien sabe que podría causar esto?

Logré reproducir el error en un pequeño ejemplo autocontenido (que también puede ver aquí:http://nbviewer.ipython.org/3714142/):

import numpy as np
from pandas import DataFrame
import datetime
from pylab import *

test = DataFrame({'x' : [datetime.datetime(2012,9,10) + datetime.timedelta(n) for n in range(10)], 
                  'y' : range(10)})

Ahora si tramo:

plot(test['x'][0:5])

No hay problema, pero cuando graficamos:

plot(test['x'][5:10])

Obtengo el KeyError a continuación (y el mensaje de error no es muy útil para mí). Estasolo pasa con datetime columnas, no con otras columnas (por lo que he experimentado). P.ej.plot(test['y'][5:10]) no es un problema.

Hay un mensaje de error:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-7-aa076e3fc4e0> in <module>()
----> 1 plot(test['x'][5:10])

C:\Python27\lib\site-packages\matplotlib\pyplot.pyc in plot(*args, **kwargs)
   2456         ax.hold(hold)
   2457     try:
-> 2458         ret = ax.plot(*args, **kwargs)
   2459         draw_if_interactive()
   2460     finally:

C:\Python27\lib\site-packages\matplotlib\axes.pyc in plot(self, *args, **kwargs)
   3846         lines = []
   3847 
-> 3848         for line in self._get_lines(*args, **kwargs):
   3849             self.add_line(line)
   3850             lines.append(line)

C:\Python27\lib\site-packages\matplotlib\axes.pyc in _grab_next_args(self, *args, **kwargs)
    321                 return
    322             if len(remaining) <= 3:
--> 323                 for seg in self._plot_args(remaining, kwargs):
    324                     yield seg
    325                 return

C:\Python27\lib\site-packages\matplotlib\axes.pyc in _plot_args(self, tup, kwargs)
    298             x = np.arange(y.shape[0], dtype=float)
    299 
--> 300         x, y = self._xy_from_xy(x, y)
    301 
    302         if self.command == 'plot':

C:\Python27\lib\site-packages\matplotlib\axes.pyc in _xy_from_xy(self, x, y)
    215         if self.axes.xaxis is not None and self.axes.yaxis is not None:
    216             bx = self.axes.xaxis.update_units(x)
--> 217             by = self.axes.yaxis.update_units(y)
    218 
    219             if self.command!='plot':

C:\Python27\lib\site-packages\matplotlib\axis.pyc in update_units(self, data)
   1277         neednew = self.converter!=converter
   1278         self.converter = converter
-> 1279         default = self.converter.default_units(data, self)
   1280         #print 'update units: default=%s, units=%s'%(default, self.units)
   1281         if default is not None and self.units is None:

C:\Python27\lib\site-packages\matplotlib\dates.pyc in default_units(x, axis)
   1153         'Return the tzinfo instance of *x* or of its first element, or None'
   1154         try:
-> 1155             x = x[0]
   1156         except (TypeError, IndexError):
   1157             pass

C:\Python27\lib\site-packages\pandas\core\series.pyc in __getitem__(self, key)
    374     def __getitem__(self, key):
    375         try:
--> 376             return self.index.get_value(self, key)
    377         except InvalidIndexError:
    378             pass

C:\Python27\lib\site-packages\pandas\core\index.pyc in get_value(self, series, key)
    529         """
    530         try:
--> 531             return self._engine.get_value(series, key)
    532         except KeyError, e1:
    533             if len(self) > 0 and self.inferred_type == 'integer':

C:\Python27\lib\site-packages\pandas\_engines.pyd in pandas._engines.IndexEngine.get_value (pandas\src\engines.c:1479)()

C:\Python27\lib\site-packages\pandas\_engines.pyd in pandas._engines.IndexEngine.get_value (pandas\src\engines.c:1374)()

C:\Python27\lib\site-packages\pandas\_engines.pyd in pandas._engines.DictIndexEngine.get_loc (pandas\src\engines.c:2498)()

C:\Python27\lib\site-packages\pandas\_engines.pyd in pandas._engines.DictIndexEngine.get_loc (pandas\src\engines.c:2460)()

KeyError: 0