How to increase the thickness of error line in a matplotlib bar chart?

Question

Please refer the minimum working example here.

The bar chart is plotted as shown below but I can't find a way to increase the thickness of the error lines. The elinewidth option is not available in ax.bar

> rects1 = ax.bar(..., elinewidth=3)

AttributeError: Unknown property elinewidth

The following links require the use of ax.errorbar()

• Change errorbar size
• How to set the line width of error bar caps, in matplotlib?

But is there an option that can be supplied directly to ax.bar()?

Answer 1

You can use the error_kw parameters as follows:

error_kw=dict(lw=5, capsize=5, capthick=3)

So in the example, it would be:

import numpy as np
import matplotlib.pyplot as plt

N = 5
men_means = (20, 35, 30, 35, 27)
men_std = (2, 3, 4, 1, 2)

ind = np.arange(N)  # the x locations for the groups
width = 0.35       # the width of the bars

fig, ax = plt.subplots()
rects1 = ax.bar(ind, men_means, width, color='r', yerr=men_std, error_kw=dict(lw=5, capsize=5, capthick=3))

women_means = (25, 32, 34, 20, 25)
women_std = (3, 5, 2, 3, 3)
rects2 = ax.bar(ind + width, women_means, width, color='y', yerr=women_std, error_kw=dict(lw=5, capsize=5, capthick=3))

# add some text for labels, title and axes ticks
ax.set_ylabel('Scores')
ax.set_title('Scores by group and gender')
ax.set_xticks(ind + width / 2)
ax.set_xticklabels(('G1', 'G2', 'G3', 'G4', 'G5'))

ax.legend((rects1[0], rects2[0]), ('Men', 'Women'))


def autolabel(rects):
    """
    Attach a text label above each bar displaying its height
    """
    for rect in rects:
        height = rect.get_height()
        ax.text(rect.get_x() + rect.get_width() / 2, 
                1.05 * height,
                f'{height:.0f}',
                ha='center', va='bottom')

autolabel(rects1)
autolabel(rects2)

plt.show()

Giving you:

---

An improvement to this would be to display the values above each of the error bars. This can be done by first obtaining the error bar heights as follows:

import numpy as np
import matplotlib.pyplot as plt

N = 5
men_means = (20, 35, 30, 35, 27)
men_std = (2, 3, 4, 1, 2)

ind = np.arange(N)  # the x locations for the groups
width = 0.35        # the width of the bars

fig, ax = plt.subplots()
rects1 = ax.bar(ind, men_means, width, color='r', yerr=men_std, error_kw=dict(lw=5, capsize=5, capthick=3))

women_means = (25, 32, 34, 20, 25)
women_std = (3, 5, 2, 3, 3)
rects2 = ax.bar(ind + width, women_means, width, color='y', yerr=women_std, error_kw=dict(lw=5, capsize=5, capthick=3))

# add some text for labels, title and axes ticks
ax.set_ylabel('Scores')
ax.set_title('Scores by group and gender')
ax.set_xticks(ind + width / 2)
ax.set_xticklabels(('G1', 'G2', 'G3', 'G4', 'G5'))

ax.set_ylim(0, 45)  # Add space for errorbar height
ax.legend((rects1[0], rects2[0]), ('Men', 'Women'))


def autolabel(rects):
    """
    Attach a text label above each bar displaying its height
    """

    data_line, capline, barlinecols = rects.errorbar

    for err_segment, rect in zip(barlinecols[0].get_segments(), rects):
        height = err_segment[1][1]  # Use height of error bar

        ax.text(rect.get_x() + rect.get_width() / 2, 
                1.05 * height,
                f'{height:.0f}',
                ha='center', va='bottom')

autolabel(rects1)
autolabel(rects2)

plt.show()

Giving you:

Note: The y axis limit would need to be calculated.