问题描述
当我尝试绘制其中带有日期时间的pandas DataFrame列的切片时，出现KeyError.有人知道是什么原因造成的吗?
I get a KeyError when I try to plot a slice of a pandas DataFrame column with datetimes in it. Does anybody know what could cause this?
我设法通过一个独立的示例重现了该错误(您也可以在此处查看: http://nbviewer.ipython. org/3714142/):
I managed to reproduce the error in a little self contained example (which you can also view here: 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)})
现在，如果我绘图:
plot(test['x'][0:5])
没有问题，但是当我绘图时:
there is not problem, but when I plot:
plot(test['x'][5:10])
我在下面看到KeyError(并且错误消息对我不是很有帮助).这仅适用于datetime 列，不适用于其他列(据我所知).例如. plot(test['y'][5:10])没问题.
I get the KeyError below (and the error message is not very helpfull to me). This only happens with datetime columns, not with other columns (as far as I experienced). E.g. plot(test['y'][5:10]) is not a problem.
其他错误消息:
---------------------------------------------------------------------------
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
推荐答案
HYRY解释了为什么会收到KeyError.要使用matplotlib使用切片进行绘图，您可以执行以下操作:
HYRY explained why you get the KeyError.To plot with slices using matplotlib you can do:
In [157]: plot(test['x'][5:10].values)
Out[157]: [<matplotlib.lines.Line2D at 0xc38348c>]
In [158]: plot(test['x'][5:10].reset_index(drop=True))
Out[158]: [<matplotlib.lines.Line2D at 0xc37e3cc>]
x，y用0.7.3一口气绘制
x, y plotting in one go with 0.7.3
In [161]: test[5:10].set_index('x')['y'].plot()
Out[161]: <matplotlib.axes.AxesSubplot at 0xc48b1cc>
这篇关于使用日期时间绘制切片的 pandas 数据框时发生KeyError的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！