爲什麼KeyError用matplotlib繪製熊貓數據框？

Question

我有這個數據幀：

 date_obj  col1  col2  col3  col4 
40038 2012-11-19 1.000 0.831856 0.986209 0.843919 
40039 2012-11-20 2.015 0.521764 1.177320 0.938245 
40040 2012-11-21 1.160 1.645345 1.964620 4.536440 
40041 2012-11-22 3.171 2.444018 2.931550 3.737840 
40042 2012-11-23 4.563 3.208111 3.587250 2.434040 
40043 2012-11-24 5.379 3.863732 3.824540 1.634780 
40044 2012-11-26 1.125 20.756739 4.162820 23.552100 
40045 2012-11-27 3.340 5.369354 4.535090 1.129290 
40046 2012-11-28 5.463 12.185730 8.102790 1.224300 
40047 2012-11-29 6.596 14.328685 9.271000 24.655600 
40048 2012-11-30 31.544 13.513497 12.103400 21.273500 
40049 2012-12-01 24.921 26.144050 16.256200 13.883100 
40050 2012-12-03 5.488 2.581351 7.220790 3.349450 
40051 2012-12-04 6.977 5.893819 5.548870 2.948770 
40052 2012-12-05 7.115 6.533022 5.863820 2.517030 
40053 2012-12-06 5.842 8.754232 7.518660 1.447940 
40054 2012-12-07 6.346 12.018631 10.263100 11.837400 
40055 2012-12-08 17.666 4.548846 10.610400 11.110800 
40056 2012-12-10 4.300 2.823566 1.475000 1.989210 
40057 2012-12-11 2.415 2.436319 2.677440 2.908270 
40058 2012-12-12 2.319 2.121092 3.455550 3.890480 
40059 2012-12-13 1.000 1.633918 3.858540 4.316940 
40060 2012-12-14 2.238 1.688475 5.065990 5.267850 
40061 2012-12-15 1.798 2.621267 7.175370 6.957340 

我嘗試繪製它以下列方式：

plt.figure(figsize=(17, 10)) 
plt.setp(plt.xticks()[1], rotation=45) 
plt.plot_date(df_cut['date_obj'],df_cut['col1'], color='black', linestyle='-', markersize=3, linewidth=2) 
plt.plot_date(df_cut['date_obj'],df_cut['col2'], color='red', linestyle='-', markersize=3) 
plt.plot_date(df_cut['date_obj'],df_cut['col3'], color='green', linestyle='-', markersize=3) 
plt.plot_date(df_cut['date_obj'],df_cut['col4'], color='blue', linestyle='-', markersize=3) 

結果我得到一個錯誤：

--------------------------------------------------------------------------- 
KeyError         Traceback (most recent call last) 
<ipython-input-544-1b8650d1e7e7> in <module>() 
/ipython/local/lib/python2.7/site-packages/matplotlib/pyplot.pyc in plot_date(x, y, fmt, tz, xdate, ydate, hold, **kwargs) 
    2850  try: 
    2851   ret = ax.plot_date(x, y, fmt=fmt, tz=tz, xdate=xdate, ydate=ydate, 
-> 2852       **kwargs) 
    2853   draw_if_interactive() 
    2854  finally: 
ipython/local/lib/python2.7/site-packages/matplotlib/axes.pyc in plot_date(self, x, y, fmt, tz, xdate, ydate, **kwargs) 
    4061   if not self._hold: self.cla() 
    4062 
-> 4063   ret = self.plot(x, y, fmt, **kwargs) 
    4064 
    4065   if xdate: 
ipython/local/lib/python2.7/site-packages/matplotlib/axes.pyc in plot(self, *args, **kwargs) 
    3994   lines = [] 
    3995 
-> 3996   for line in self._get_lines(*args, **kwargs): 
    3997    self.add_line(line) 
    3998    lines.append(line) 
ipython/local/lib/python2.7/site-packages/matplotlib/axes.pyc in _grab_next_args(self, *args, **kwargs) 
    328     return 
    329    if len(remaining) <= 3: 
--> 330     for seg in self._plot_args(remaining, kwargs): 
    331      yield seg 
    332     return 
ipython/local/lib/python2.7/site-packages/matplotlib/axes.pyc in _plot_args(self, tup, kwargs) 
    306    x = np.arange(y.shape[0], dtype=float) 
    307 
--> 308   x, y = self._xy_from_xy(x, y) 
    309 
    310   if self.command == 'plot': 
python/local/lib/python2.7/site-packages/matplotlib/axes.pyc in _xy_from_xy(self, x, y) 
    222  def _xy_from_xy(self, x, y): 
    223   if self.axes.xaxis is not None and self.axes.yaxis is not None: 
--> 224    bx = self.axes.xaxis.update_units(x) 
    225    by = self.axes.yaxis.update_units(y) 
    226 
ipython/local/lib/python2.7/site-packages/matplotlib/axis.pyc in update_units(self, data) 
    1299   neednew = self.converter != converter 
    1300   self.converter = converter 
-> 1301   default = self.converter.default_units(data, self) 
    1302   #print 'update units: default=%s, units=%s'%(default, self.units) 
    1303   if default is not None and self.units is None: 
ipython/local/lib/python2.7/site-packages/matplotlib/dates.pyc in default_units(x, axis) 
    1156   'Return the tzinfo instance of *x* or of its first element, or None' 
    1157   try: 
-> 1158    x = x[0] 
    1159   except (TypeError, IndexError): 
    1160    pass 
ipython/local/lib/python2.7/site-packages/pandas/core/series.pyc in __getitem__(self, key) 
    611  def __getitem__(self, key): 
    612   try: 
--> 613    return self.index.get_value(self, key) 
    614   except InvalidIndexError: 
    615    pass 
ipython/local/lib/python2.7/site-packages/pandas/core/index.pyc in get_value(self, series, key) 
    761   """ 
    762   try: 
--> 763    return self._engine.get_value(series, key) 
    764   except KeyError, e1: 
    765    if len(self) > 0 and self.inferred_type == 'integer': 

有什麼奇怪，這段代碼適用於某些數據框架，有些則不適用。數據框架的結構沒有差異。它們之間的唯一區別僅在於它們包含的值。

有沒有人請幫我解決這個問題？

Answer 1

Dataframe將日期存儲爲numpy.datetime64對象，而不是python datetime對象。

此外，matplotlib.plot_date使用它自己的日期數值表示。

你可以提醒你的數據是這樣的：

plt.plot_date(matplotlib.dates.date2num(pandas.to_datetime(df_cut['date_obj'].values)),df_cut['col1'].values, color='black', linestyle='-', markersize=3, linewidth=2) 

或者你可以定義列「date_obj」作爲您的數據的索引：

df0 = pd.DataFrame.from_records(YourDataSource, columns=['date_obj','col1','col2','col3','col4'],index='date_obj') 

，然後只需用大熊貓的情節（）屬性：

df0['col1'].plot()