errorbar fails with pandas data frame

[david-zwicker]

plt.errorbar seems to dislike pandas Dataframes since matplotlib 1.5.0.

Here is the full code:

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

df = pd.DataFrame(np.random.rand(10, 2))
plt.errorbar(df[0], df[1], 'o')

which produces the following error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-21-8f3d736d3f20> in <module>()
----> 1 plt.errorbar(df[0], df[1], 'o')

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/pyplot.pyc in errorbar(x, y, yerr, xerr, fmt, ecolor, elinewidth, capsize, barsabove, lolims, uplims, xlolims, xuplims, errorevery, capthick, hold, data, **kwargs)
   2828                           xlolims=xlolims, xuplims=xuplims,
   2829                           errorevery=errorevery, capthick=capthick, data=data,
-> 2830                           **kwargs)
   2831     finally:
   2832         ax.hold(washold)

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/__init__.pyc in inner(ax, *args, **kwargs)
   1809                     warnings.warn(msg % (label_namer, func.__name__),
   1810                                   RuntimeWarning, stacklevel=2)
-> 1811             return func(ax, *args, **kwargs)
   1812         pre_doc = inner.__doc__
   1813         if pre_doc is None:

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/axes/_axes.pyc in errorbar(self, x, y, yerr, xerr, fmt, ecolor, elinewidth, capsize, barsabove, lolims, uplims, xlolims, xuplims, errorevery, capthick, **kwargs)
   2961                 # using list comps rather than arrays to preserve units
   2962                 lower = [thisy - thiserr for (thisy, thiserr)
-> 2963                          in cbook.safezip(y, yerr)]
   2964                 upper = [thisy + thiserr for (thisy, thiserr)
   2965                          in cbook.safezip(y, yerr)]

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/cbook.pyc in safezip(*args)
   1492     for i, arg in enumerate(args[1:]):
   1493         if len(arg) != Nx:
-> 1494             raise ValueError(_safezip_msg % (Nx, i + 1, len(arg)))
   1495     return list(zip(*args))
   1496 

ValueError: In safezip, len(args[0])=10 but len(args[1])=1

Interestingly, the code works if I replace errorbar by plot.

[tacaswell]

This is not a pandas problem, mpl is trying to use 'o' as the yerr input which obviously does not work 😉 .

Try

plt.errorbar(df[0], df[1], marker='o')

[david-zwicker]

Uhh, sorry, my mistake. I should have read the documentation more closely. Thanks for the quick help!

[tacaswell]

No worries, the easy ones make me happy.