Car crash chart: a step-by-step guide

tutorial
mpl-pe-fancy-bar
mpl-visual-context
Author

Jae-Joon Lee

Published

November 7, 2024

Modified

November 7, 2024

Decorate your matplotlib bar charts : step-by-step guide

This is another guide to decorate matplotlib bar charts. We will basically apply path effects, using packages like mpl-visual-context and mpl_pe_fancy_bar. And we will do it step by step.

Code 
import numpy as np
import seaborn as sns
import matplotlib.pyplot as plt
sns.set_theme(style="whitegrid")

# Load the example car crash dataset
crashes = sns.load_dataset("car_crashes").sort_values("total", ascending=False).iloc[:10]

# Initialize the matplotlib figure
fig, ax = plt.subplots(num=1, clear=True, figsize=(5, 4), layout="constrained")
# fig, ax = plt.subplots(num=1, clear=True, layout="constrained")

# Plot the total crashes
sns.set_color_codes("pastel")
sns.barplot(x="total", y="abbrev", data=crashes,
            label="Total", color="b")

# Plot the crashes where alcohol was involved
sns.set_color_codes("muted")
sns.barplot(x="alcohol", y="abbrev", data=crashes,
            label="Alcohol-involved", color="b")

# Add a legend and informative axis label
ax.legend(ncol=2, loc="lower right", frameon=True,
          bbox_to_anchor=[1, 1])

ax.set(xlim=(0, 24.8),
       ylim=(9.6, -0.6),
       ylabel="",
       xlabel="Automobile collisions per billion miles")

sns.despine(left=True, bottom=True)

import mpl_visual_context.patheffects as pe
from mpl_pe_fancy_bar import BarToRoundBar
from mpl_visual_context.patheffects_shadow import ShadowPath

round_bar = BarToRoundBar(orientation="horizontal", dh=0.5)
shadow = ShadowPath(115, 3)

from svgpath2mpl import parse_path

# car icon from https://fontawesome.com/icons/car?f=classic&s=solid
# 512 x 512
s_car = "M135.2 117.4L109.1 192H402.9l-26.1-74.6C372.3 104.6 360.2 96 346.6 96H165.4c-13.6 0-25.7 8.6-30.2 21.4zM39.6 196.8L74.8 96.3C88.3 57.8 124.6 32 165.4 32H346.6c40.8 0 77.1 25.8 90.6 64.3l35.2 100.5c23.2 9.6 39.6 32.5 39.6 59.2V400v48c0 17.7-14.3 32-32 32H448c-17.7 0-32-14.3-32-32V400H96v48c0 17.7-14.3 32-32 32H32c-17.7 0-32-14.3-32-32V400 256c0-26.7 16.4-49.6 39.6-59.2zM128 288a32 32 0 1 0 -64 0 32 32 0 1 0 64 0zm288 32a32 32 0 1 0 0-64 32 32 0 1 0 0 64z"
s_wine = "M32 0C19.1 0 7.4 7.8 2.4 19.8s-2.2 25.7 6.9 34.9L224 269.3 224 448l-64 0c-17.7 0-32 14.3-32 32s14.3 32 32 32l96 0 96 0c17.7 0 32-14.3 32-32s-14.3-32-32-32l-64 0 0-178.7L502.6 54.6c9.2-9.2 11.9-22.9 6.9-34.9S492.9 0 480 0L32 0zM173.3 128l-64-64 293.5 0-64 64-165.5 0z"

icon_car = parse_path(s_car)
icon_wine = parse_path(s_wine)

from mpl_pe_fancy_bar.bar_with_icon import Icon, BarWithIcon

with_icon_car = BarWithIcon(Icon((512, 512), icon_car), orientation="horizontal", scale=0.5, dh=0.6)
with_icon_wine = BarWithIcon(Icon((512, 512), icon_wine), orientation="horizontal", scale=0.5, dh=0.6)

pe1 = [
    round_bar,
    round_bar | pe.ClipPathSelf() | shadow | pe.HLSModify(l="70%"),
    with_icon_car | shadow | pe.HLSModify(l="50%"),
    with_icon_car | pe.FillColor("w")
]
for p in ax.containers[0]:
    p.set_path_effects(pe1)

pe2 = [
    round_bar | pe.FillOnly(),
    with_icon_wine | pe.FillColor("w")
]
for p in ax.containers[1]:
    p.set_path_effects(pe2)

from mpl_visual_context.axes_panel import InsetDivider, add_panel
from mpl_visual_context.legend_helper import (
    extract_offset_boxes_from_legend,
)
from matplotlib.offsetbox import HPacker
from matplotlib.offsetbox import AnchoredOffsetbox

divider = InsetDivider(ax)

panel = add_panel(divider, "left", "ticklabels", pad=0.0)
legend_panel = add_panel(divider, "top", "empty", pad=0.0)

leg_title, oblist = extract_offset_boxes_from_legend(ax.legend_)

pack = HPacker(pad=0.0, sep=10, children=oblist)
box = AnchoredOffsetbox("upper center", child=pack, pad=0, frameon=False)
ax.legend_.remove()

legend_panel.add_artist(box)
legend_panel.add_to_extent_list(box)
legend_panel.grid(False)

panel.set_axis_off()

fc = "gold"
fig.patch.set_fc(fc)
ax.patch.set_visible(False) # fc(fc)

A seaborn barplot : a starting point

The starting plot is based on this seaborn example

import numpy as np
import seaborn as sns
import matplotlib.pyplot as plt
sns.set_theme(style="whitegrid")

# Load the example car crash dataset
crashes = sns.load_dataset("car_crashes").sort_values("total", ascending=False).iloc[:10]

# Initialize the matplotlib figure
fig, ax = plt.subplots(num=1, clear=True, figsize=(5, 4), layout="constrained")
fc = "gold"
fig.patch.set_fc(fc)
ax.patch.set_visible(False) # fc(fc)

# Plot the total crashes
sns.set_color_codes("pastel")
sns.barplot(x="total", y="abbrev", data=crashes,
            label="Total", color="b")

# Plot the crashes where alcohol was involved
sns.set_color_codes("muted")
sns.barplot(x="alcohol", y="abbrev", data=crashes,
            label="Alcohol-involved", color="b")

# Add a legend and informative axis label
ax.legend(ncol=2, loc="lower right", frameon=True,
          bbox_to_anchor=[1, 1])

ax.set(xlim=(0, 24.8),
       ylim=(9.6, -0.6),
       ylabel="",
       xlabel="Automobile collisions per billion miles")

sns.despine(left=True, bottom=True)

Make it round

mpl-pe-fancy-bar module contains patheffects that transform a simple rectangle path to a more complicated one. Below, we will use BarToRoundBar that transform a rectabngle to a rounded one. We will also use patheffects from the mpl-visual-context. FillOnly will only fill the path without a stroke.

import mpl_visual_context.patheffects as pe
from mpl_pe_fancy_bar import BarToRoundBar

bar_containers_total = ax.containers[0]
bar_containers_alcohol = ax.containers[1]

round_bar = BarToRoundBar(orientation="horizontal", dh=0.5)

pe1 = [
    round_bar,
]
for p in bar_containers_total:
    p.set_path_effects(pe1)

pe2 = [
    round_bar | pe.FillOnly(),
]
for p in bar_containers_alcohol:
    p.set_path_effects(pe2)

Simple debossing effect

We will add naive debossing effect by adding a shadow effect that is clipped by the path itself. Note the order of clipping and the shdow. The clip path effect will copy the current path, so the clipping path won’t be affected by any path transformation in the downstream. The shadow patheffect will result in the path that can be filled to give some shadow effect (e.g., this example )

from mpl_visual_context.patheffects_shadow import ShadowPath
shadow = ShadowPath(115, 3)

pe1 = [
    round_bar,
    round_bar | pe.ClipPathSelf() | shadow | pe.HLSModify(l="70%"),
]
for p in bar_containers_total:
    p.set_path_effects(pe1)

pe2 = [
    round_bar | pe.FillOnly(),
]
for p in bar_containers_alcohol:
    p.set_path_effects(pe2)

Add SVG Icons

Let’s add car icons to the bars. There could be different ways. We use BarWithIcon class. The advantage of this is that the size of icon will automatically scale relative to the width of the bars.

from svgpath2mpl import parse_path

# car icon from https://fontawesome.com/icons/car?f=classic&s=solid
# 512 x 512
s_car = "M135.2 117.4L109.1 192H402.9l-26.1-74.6C372.3 104.6 360.2 96 346.6 96H165.4c-13.6 0-25.7 8.6-30.2 21.4zM39.6 196.8L74.8 96.3C88.3 57.8 124.6 32 165.4 32H346.6c40.8 0 77.1 25.8 90.6 64.3l35.2 100.5c23.2 9.6 39.6 32.5 39.6 59.2V400v48c0 17.7-14.3 32-32 32H448c-17.7 0-32-14.3-32-32V400H96v48c0 17.7-14.3 32-32 32H32c-17.7 0-32-14.3-32-32V400 256c0-26.7 16.4-49.6 39.6-59.2zM128 288a32 32 0 1 0 -64 0 32 32 0 1 0 64 0zm288 32a32 32 0 1 0 0-64 32 32 0 1 0 0 64z"

s_wine = "M32 0C19.1 0 7.4 7.8 2.4 19.8s-2.2 25.7 6.9 34.9L224 269.3 224 448l-64 0c-17.7 0-32 14.3-32 32s14.3 32 32 32l96 0 96 0c17.7 0 32-14.3 32-32s-14.3-32-32-32l-64 0 0-178.7L502.6 54.6c9.2-9.2 11.9-22.9 6.9-34.9S492.9 0 480 0L32 0zM173.3 128l-64-64 293.5 0-64 64-165.5 0z"

icon_car = parse_path(s_car)
icon_wine = parse_path(s_wine)

from matplotlib.path import Path
from mpl_pe_fancy_bar.bar_with_icon import Icon, BarWithIcon

with_car = BarWithIcon(Icon((512, 512), icon_car),
                       orientation="horizontal", scale=0.5, dh=0.6)
with_wine = BarWithIcon(Icon((512, 512), icon_wine),
                        orientation="horizontal", scale=0.5, dh=0.6)

pe1 = [
    round_bar,
    round_bar | pe.ClipPathSelf() | shadow | pe.HLSModify(l="70%"),
    with_car | shadow | pe.HLSModify(l="50%"),
    with_car | pe.FillColor("w")
]
for p in bar_containers_total:
    p.set_path_effects(pe1)

pe2 = [
    round_bar | pe.FillOnly(),
    with_wine | pe.FillColor("w")
]
for p in bar_containers_alcohol:
    p.set_path_effects(pe2)

We will also change the look of legend. We will use panel feature of mpl_visual_context, which we won’t address its detail. In short, panel is an axes that is located next to the main axes, which is meant to display ticks and labels as annotations for more flexibility. Take a look at these examples (ex1 and ex2).

from mpl_visual_context.axes_panel import InsetDivider, add_panel
from mpl_visual_context.legend_helper import (
    extract_offset_boxes_from_legend,
)
from matplotlib.offsetbox import HPacker
from matplotlib.offsetbox import AnchoredOffsetbox

divider = InsetDivider(ax)

panel = add_panel(divider, "left", "ticklabels", pad=0.0)
legend_panel = add_panel(divider, "top", "empty", pad=0.0)

leg_title, oblist = extract_offset_boxes_from_legend(ax.legend_)

pack = HPacker(pad=0.0, sep=10, children=oblist)
box = AnchoredOffsetbox("upper center", child=pack, pad=0, frameon=False)
ax.legend_.remove()

legend_panel.add_artist(box)
legend_panel.add_to_extent_list(box)
legend_panel.grid(False)

panel.set_axis_off()