Matplotlib Errorbar Caps Missing

Question

I'm attempting to create a scatter plot with errorbars in matplotlib. The following is an example of what my code looks like:

import matplotlib.pyplot as plt
import numpy as np
import random

x = np.linspace(1,2,10)
y = np.linspace(2,3,10)
err = [random.uniform(0,1) for i in range(10)]

plt.errorbar(x, y,
       yerr=err,
       marker='o',
       color='k',
       ecolor='k',
       markerfacecolor='g',
       label="series 2",
       capsize=5,
       linestyle='None')
plt.show()

The problem is the plot which is output contains no caps at all! enter image description here

For what it's worth, I'm on Ubuntu 13.04, Python 2.7.5 |Anaconda 1.6.1 (64-bit)|, and Matplotlib 1.2.1.

Could this be a hidden rcparam that needs to be overwritten?

did you change anything to make your background gray? I am wondering if you are having zorder issues (related to http://stackoverflow.com/questions/14003572/how-to-force-errorbars-to-render-last-with-matplotlib/14007175#14007175). The patch for that issue is in 1.3, but not 1.2.1 — tacaswell, Aug 25 '13 at 23:04
Your code runs correctly on my system, I suspect that in making the graphs look awful (yes, I know it is subjective) you broke something. We need to see your rcparams to debug this. — tacaswell, Aug 25 '13 at 23:08
Yes, Actually I am using a matplotlibrc file which is significantly altered from what it is by default. What section of the file are you needing to look at? — astromax, Aug 26 '13 at 02:17
does this work as expected if you use the default `matplotlibrc` file (just rename yours before you start up python)? — tacaswell, Aug 26 '13 at 03:08

score 25 · Accepted Answer · edited May 23 '17 at 11:54

25

What worked for me was adding this (as per: How to set the line width of error bar caps, in matplotlib):

(_, caps, _) = plt.errorbar(x,y, yerr=err, capsize=20, elinewidth=3)

for cap in caps:
    cap.set_color('red')
    cap.set_markeredgewidth(10)

edited May 23 '17 at 11:54

Community

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answered Aug 26 '13 at 02:28

astromax

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Not particularly. I've tried to understand it, but it the syntax seems to be confusing me. I know (_,caps,_) is producing a tuple of tuples, however, set_color() and set_markeredgewidth() I am unfamiliar with. – astromax Aug 28 '13 at 02:42
They do exactly what they sound like, set the color and the the edge width of the markers. http://matplotlib.org/api/artist_api.html#matplotlib.lines.Line2D.set_color http://matplotlib.org/api/artist_api.html#matplotlib.lines.Line2D.set_markeredgewidth – tacaswell Aug 28 '13 at 02:55
I was more asking did you figure out what you changed in you `matplotlibrc` file that broke it. – tacaswell Aug 28 '13 at 02:55
For me the main fault was for some inexplicable reason `capsize`. Instead of `set_markeredgewidth` and `set_color`, you should be able to use the `capthick` and `ecolor` arguments in the [`errorbar` call](https://matplotlib.org/api/_as_gen/matplotlib.pyplot.errorbar.html). – mxmlnkn Mar 19 '18 at 15:50

score 16 · Answer 2 · edited Nov 15 '19 at 17:33

16

It has to do with the rcParams in matplotlib. To solve it, add the following lines at the beginning of your script:

import matplotlib
matplotlib.rcParams.update({'errorbar.capsize': 2})

It also works with plt.bar().

edited Nov 15 '19 at 17:33

Neuron

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answered Apr 15 '18 at 04:21

Lucho

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score 16 · Answer 3 · answered Feb 01 '19 at 21:22

16

Slight simplification of astromax's answer:

plt.errorbar(x,y, yerr=err, capsize=20, elinewidth=3, markeredgewidth=10)

It seems that somehow markeredgewidth is defaulting to 0 sometimes.

answered Feb 01 '19 at 21:22

aquirdturtle

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Matplotlib Errorbar Caps Missing

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