How to set the line width of error bar caps

Question

How can the line width of the error bar caps in Matplotlib be changed?

I tried the following code:

(_, caplines, _) = matplotlib.pyplot.errorbar(
    data['distance'], data['energy'], yerr=data['energy sigma'],
    capsize=10, elinewidth=3)

for capline in caplines:
    capline.set_linewidth(10)
    capline.set_color('red')

pp.draw()

Unfortunately, this updates the color of the caps, but does not update the line width of the caps!

The resulting effect is similar to the “fat error bar lines / thin caps” in the following image:
enter image description here

It would be nice to have “fat” bar caps, in the case; how can this be done, in Matplotlib? Drawing the bar caps “manually”, one by one with plot() would work, but a simpler alternative would be best.

Asked By: Eric O Lebigot

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Source

Answer 1

EOL, you were very close..,

distance = [1,3,7,9]
energy = [10,20,30,40]
sigma = [1,3,2,5]

(_, caps, _) = plt.errorbar(distance, energy, sigma, capsize=20, elinewidth=3)

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

plt.show

enter image description here

set_markeredgewidth sets the width of the cap lines.

Matplotlib objects have so many attributes that often it is difficult to remember the right ones for a given object. IPython is a very useful tool for introspecting matplotlib. I used it to analyze the properties of the 2Dlines correponding to the error cap lines and I found that and other marker properties.

Cheers

Answered By: joaquin

Answer 2

This is based on @joaquin’s answer, but a little more concise (if you just want plain error caps with no special styling):

distance = [1,3,7,9]
energy = [10,20,30,40]
sigma = [1,3,2,5]

plt.errorbar(distance, 
    energy, 
    sigma, 
    capsize=5, 
    elinewidth=2,
    markeredgewidth=2)

Answered By: John

How to set the line width of error bar caps

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