CODEWITHSUNDEEP
pythonnumpymatplotlib
Nick Duddy
Nick Duddy

Reputation: 1000

ValueError: invalid literal for float(): 17/08/2015

I'm getting this error "ValueError: invalid literal for float(): 17/08/2015". This is the last row in the file I'm reading and it follows the same format as the others. The code for the script is below.

I'm wondering. Is the error actually occurring throughout the file but it's being flagged as the only error because it's the last of the errors, if that makes sense to anyone.

    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'

Upvotes: 0

Views: 7728

Answers (1)

thomas
thomas

Reputation: 1813

The error occurs because you are trying to plot some stuff with dates as strings on the x-axis while plt.plot() expects numerical values. Hence it fails when it tries to convert '17/08/2015' to a float, which cannot work.

You need to convert your x-values to datetime objects and then use plt.plot_date, which is for example demonstrated here.

Upvotes: 5

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