Broken Axis Slash Marks Inside Bar Chart In Matplotlib?

I've seen matplotlib examples of placing the broken axis slash marks on the axes, such as this one. My questions, how can I place it where the bars are broken? Can this be done i

Solution 1:

Just to show the principle, you can put the same kind of line at every position where a bar exceeds the upper limit of the lower axes and also where a bar exceeds the lower limit of the upper axes.

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

XX = pd.Series([200,400,100,1400],index=['x1','x2','x3','x4'])
fig, (ax1,ax2) = plt.subplots(2,1,sharex=True,
                         figsize=(5,6))
ax1.spines['bottom'].set_visible(False)
ax1.tick_params(axis='x',which='both',bottom=False)
ax2.spines['top'].set_visible(False)

bs = 500
ts = 1000

ax2.set_ylim(0,bs)
ax1.set_ylim(ts,1500)
ax1.set_yticks(np.arange(1000,1501,100))

bars1 = ax1.bar(XX.index, XX.values)
bars2 = ax2.bar(XX.index, XX.values)

for tick in ax2.get_xticklabels():
    tick.set_rotation(0)
d = .015  
kwargs = dict(transform=ax1.transAxes, color='k', clip_on=False)
ax1.plot((-d, +d), (-d, +d), **kwargs)      
ax1.plot((1 - d, 1 + d), (-d, +d), **kwargs)
kwargs.update(transform=ax2.transAxes)  
ax2.plot((-d, +d), (1 - d, 1 + d), **kwargs)  
ax2.plot((1 - d, 1 + d), (1 - d, 1 + d), **kwargs)

for b1, b2 inzip(bars1, bars2):
    posx = b2.get_x() + b2.get_width()/2.if b2.get_height() > bs:
        ax2.plot((posx-3*d, posx+3*d), (1 - d, 1 + d), color='k', clip_on=False,
                 transform=ax2.get_xaxis_transform())
    if b1.get_height() > ts:
        ax1.plot((posx-3*d, posx+3*d), (- d, + d), color='k', clip_on=False,
                 transform=ax1.get_xaxis_transform())
plt.show()

It doesn't look great, but can of course be adapted with a nicer shape.

Solution 2:

I needed broken y-axis some time ago and created some code to do it. Now, I have submitted it to PyPi so that others can use it. It's far from being a final version though. Any comments are welcome, and there is also the GitHub project, in which anyone can collaborate of course. Any issue, code and anything else is welcome.

Also, consider reading the following post. It gives some good reasons why a broken y-axis might not be desirable, before deciding on using it or not. One of the main points in my opinion is that breaking the y-axis makes the sense of proportion go away entirely. As it happens with limited y-axis ranges, it can be rather confusing to see a plot like this. That said, if used, I would recommend that the audience is made aware of the strange proportions that can arise from the use of this kind of plot.

• Broken Y Axis in an Excel Chart at Peltier Tech Blog

Installing:

pip install plotinpy

Here is some example usages of the broken y-axis:

Examples

Simple broken bars

plt.figure()
pnp.plot_bars_with_breaks(
    [1, 2, 30],
    [(15, 25)]
    )
plt.savefig("img/example1.png")

Styled broken bars

plt.figure()
pnp.plot_bars_with_breaks(
    [1, 2, 30, 1000],
    [(15, 25), (50, 975)],
    style="~~",
    break_args={"hatch": '///'}
    )
plt.savefig("img/example2.png")