使用日期时间绘制切片的 Pandas 数据框时出现 KeyError
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/12406162/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
KeyError when plotting a sliced pandas dataframe with datetimes
提问by joris
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?
当我尝试绘制包含日期时间的 Pandas DataFrame 列的切片时，出现 KeyError 错误。有谁知道这可能导致什么？
I managed to reproduce the error in a little self contained example (which you can also view here: http://nbviewer.ipython.org/3714142/):
我设法在一个小的自包含示例中重现了错误（您也可以在此处查看：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)})
Now if I plot:
现在，如果我绘制：
plot(test['x'][0:5])
there is not problem, but when I plot:
没有问题，但是当我绘制时：
plot(test['x'][5:10])
I get the KeyError below (and the error message is not very helpfull to me). This only happens with datetimecolumns, not with other columns (as far as I experienced). E.g. plot(test['y'][5:10])is not a problem.
我得到下面的 KeyError （错误消息对我不是很有帮助）。这仅发生日期时间列，不能与其他列（据我所经历）。例如plot(test['y'][5:10])不是问题。
Ther error message:
错误信息：
---------------------------------------------------------------------------
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
采纳答案by Wouter Overmeire
HYRY explained why you get the KeyError. To plot with slices using matplotlib you can do:
HYRY 解释了您收到 KeyError 的原因。要使用 matplotlib 绘制切片，您可以执行以下操作：
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 plotting in one go with 0.7.3
x, y 与 0.7.3 一起绘制
In [161]: test[5:10].set_index('x')['y'].plot()
Out[161]: <matplotlib.axes.AxesSubplot at 0xc48b1cc>
回答by HYRY
Instead of calling plot(test["x"][5:10]), you can call the plot method of Series object:
plot(test["x"][5:10])您可以调用 Series 对象的 plot 方法，而不是调用：
test["x"][5:10].plot()
The reason: test["x"][5:10]is a Series object with integer index from 5 to 10. plot()try to get index 0 of it, that will cause error.
原因：test["x"][5:10]是一个整数索引从 5 到 10 的 Series 对象。plot()尝试获取它的索引 0，这将导致错误。
回答by citynorman
I encountered this error with pd.groupbyin Pandas 0.14.0 and solved it with df = df[df['col']!= 0].reset_index()
我pd.groupby在 Pandas 0.14.0 中遇到了这个错误并用df = df[df['col']!= 0].reset_index()
