ValueError:float()的无效文字:17/08/2015

Question

我收到此错误"ValueError:float()的无效文字:17/08/2015".这是我正在阅读的文件中的最后一行,它遵循与其他文件相同的格式.脚本的代码如下.

我在想.该错误是否实际发生在整个文件中,但它被标记为唯一错误,因为它是最后一个错误,如果这对任何人都有意义.

    import numpy as np
    import pandas as pd
    import matplotlib.pyplot as plt

    rankings = pd.read_csv('data/rankingunitsdata.csv', parse_dates='date')
    rankings.plot('date','rankingpos')

    x = rankings.date.values
    y = rankings.rankingpos.values

    plt.plot(x,y, 'o')
    plt.xlabel('Ranking Position')
    plt.ylabel('Date')
    plt.show()

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-15-b6d9eb0809d3> in <module>()
----> 1 plt.plot(x,y, 'o')
      2 plt.xlabel('Ranking Position')
      3 plt.ylabel('Date')
      4 plt.show()

C:\Anaconda3\lib\site-packages\matplotlib\pyplot.py in plot(*args, **kwargs)
   3097         ax.hold(hold)
   3098     try:
-> 3099         ret = ax.plot(*args, **kwargs)
   3100         draw_if_interactive()
   3101     finally:

C:\Anaconda3\lib\site-packages\matplotlib\axes\_axes.py in plot(self, *args, **kwargs)
   1372 
   1373         for line in self._get_lines(*args, **kwargs):
-> 1374             self.add_line(line)
   1375             lines.append(line)
   1376 

C:\Anaconda3\lib\site-packages\matplotlib\axes\_base.py in add_line(self, line)
   1502             line.set_clip_path(self.patch)
   1503 
-> 1504         self._update_line_limits(line)
   1505         if not line.get_label():
   1506             line.set_label('_line%d' % len(self.lines))

C:\Anaconda3\lib\site-packages\matplotlib\axes\_base.py in _update_line_limits(self, line)
   1513         Figures out the data limit of the given line, updating self.dataLim.
   1514         """
-> 1515         path = line.get_path()
   1516         if path.vertices.size == 0:
   1517             return

C:\Anaconda3\lib\site-packages\matplotlib\lines.py in get_path(self)
    872         """
    873         if self._invalidy or self._invalidx:
--> 874             self.recache()
    875         return self._path
    876 

C:\Anaconda3\lib\site-packages\matplotlib\lines.py in recache(self, always)
    573                 x = ma.asarray(xconv, np.float_)
    574             else:
--> 575                 x = np.asarray(xconv, np.float_)
    576             x = x.ravel()
    577         else:

C:\Anaconda3\lib\site-packages\numpy\core\numeric.py in asarray(a, dtype, order)
    472 
    473     """
--> 474     return array(a, dtype, copy=False, order=order)
    475 
    476 def asanyarray(a, dtype=None, order=None):

ValueError: could not convert string to float: '17/08/2015'

Answer 1

发生错误是因为您试图在x轴上绘制日期作为字符串的某些内容,同时plt.plot()期望数值.因此它在尝试转换'17/08/2015'为浮点时失败,浮点数无效.

您需要将x值转换为datetime对象,然后使用plt.plot_date,例如此处演示.