Assertion Error matplotlib when plotting a pandas read file using matplotlib error bar

Question

I am getting the error below when I try to plot the error bar of some data I read from a csv file using pandas read_csv.

ax.errorbar(x1, y1, yerr = std1, marker='d',color='y', label='y1')
File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 5762, in errorbar
xo, _ = xywhere(x, lower, everymask)
File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 5669, in xywhere
assert len(xs) == len(ys)
AssertionError

the code I used is:

 ress=pd.read_csv('/path/myfile', delimiter=',',skiprows=[0],header=None,dtype=None)
 x1=ress[[0]]
 y1=ress[[3]]
 std1=ress[[4]]

 ax=plt.subplot(111)
 ax.errorbar(x1,y1,yerr=std1,marker='d',color='y',label='y1')

I thought at first that x1 and y1 aren't of the same dimensions so I printed x1.shape, y1.shape, and std1.shape and all of them where (11,1). P.S. (11,1) is a correct way of representing my data.

Do you know why I am getting this error?

Thanks in advance

Can you print x1, y1, and std1 and show their content here. — Mike Müller
– Mike Müller, Commented Nov 27, 2015 at 22:41

DSM · Accepted Answer · 2015-11-27 22:41:51Z

1

The error message is a little misleading here. Because you're using

x1 = ress[[0]]

instead of

x1 = ress[0]

etc., you're passing errorbar a DataFrame (a 2D object of shape (11,1)) instead of a Series (a 1D object of shape (11,)). This is confusing matplotlib. Remove the extra brackets and it should work. For example, we have

>>> ress = pd.DataFrame({0: range(15,20), 3: range(5), 4: [2]*5})
>>> x1 = ress[[0]]
>>> y1 = ress[[3]]
>>> std1 = ress[[4]]
>>> ax = plt.subplot(111)
>>> ax.errorbar(x1,y1,yerr=std1.values,marker='d',color='y',label='y1')
Traceback (most recent call last):
[...]
    assert len(xs) == len(ys)
AssertionError

but

>>> x1,y1,std = ress[0], ress[3], ress[4]
>>> ax = plt.subplot(111)
>>> ax.errorbar(x1,y1,yerr=std1.values,marker='d',color='y',label='y1')
<Container object of 3 artists>

answered Nov 27, 2015 at 22:41

DSM

355k67 gold badges606 silver badges504 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Assertion Error matplotlib when plotting a pandas read file using matplotlib error bar

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related