22 of 100: Curved stacked bar chart in matplotlib
At the beginning of the year I challenged myself to create all 100 visualizations using python and matplotlib from the 1 dataset,100 visualizations project and I am sharing with you the code for all the visualizations.
Note: Data Viz Project is copyright Ferdio and available under a Creative Commons Attribution – Non Commercial – No Derivatives 4.0 International license. I asked Ferdio and they told me they used a Design tool to create all the plots.
Collaborate
There are a ton of improvements that can be made on the code, so let me know in the comments any improvements you make and I will update the post accordingly!
To be improved: It has a little bit of hardcoding here and there, will revisit.
This is the original viz that we are trying to recreate in matplotlib:

Import the packages
We will need the following packages:
import matplotlib.pyplot as plt
from matplotlib.patches import Arc
import numpy as np
import pandas as pd
Generate the data
We could actually go from numpy to matplotlib, but most data projects use pandas to transform the data, so I am using a pandas dataframe as the starting point.
color_dict = {"Norway": "#2B314D", "Denmark": "#A54836", "Sweden": "#5375D4", }
xy_ticklabel_color, xy_label_color, grid_color, datalabels_color ='#101628',"#101628", "#C8C9C9", "#757C85"
data = {
"year": [2004, 2022, 2004, 2022, 2004, 2022],
"countries" : [ "Denmark", "Denmark", "Norway", "Norway","Sweden", "Sweden",],
"sites": [4,10,5,8,13,15]
}
df= pd.DataFrame(data)
index | year | countries | sites |
---|---|---|---|
0 | 2004 | Sweden | 13 |
1 | 2022 | Sweden | 15 |
2 | 2004 | Denmark | 4 |
3 | 2022 | Denmark | 10 |
4 | 2004 | Norway | 5 |
5 | 2022 | Norway | 8 |
We need to create the year labels, the country code and sort.
df = df.sort_values([ 'year','sites'], ascending=False ).reset_index(drop=True)
df['ctry_code'] = df.countries.astype(str).str[:2].astype(str).str.upper()
df['year_lbl'] ="'"+df['year'].astype(str).str[-2:].astype(str)
sort_order_dict = {"Denmark":2, "Sweden":3, "Norway":1, 2004:4, 2022:5}
df = df.sort_values(by=['year','countries',], key=lambda x: x.map(sort_order_dict))
#map the colors of a dict to a dataframe
df['color']= df.countries.map(color_dict)
index | year | countries | sites | ctry_code | year_lbl | color |
---|---|---|---|---|---|---|
4 | 2004 | Norway | 5 | NO | ’04 | #2B314D |
5 | 2004 | Denmark | 4 | DE | ’04 | #A54836 |
3 | 2004 | Sweden | 13 | SW | ’04 | #5375D4 |
2 | 2022 | Norway | 8 | NO | ’22 | #2B314D |
1 | 2022 | Denmark | 10 | DE | ’22 | #A54836 |
0 | 2022 | Sweden | 15 | SW | ’22 | #5375D4 |
Define the variables:
max_sites = df[df.year == df.year.max()]['sites'].to_list()
min_sites = df[df.year == df.year.min()]['sites'].to_list()
colors = df.color.unique()
countries = df['ctry_code'].unique()
y_axis = range(3)
Plot the chart
fig, ax = plt.subplots(figsize=(10,3),sharex=True, sharey=True, facecolor = "#FFFFFF", zorder= 1)
smoothing = 100
for y_ax, max_site, min_site,color in zip(reversed(y_axis, max_sites,min_sites,colors):
x = np.linspace(0, np.pi * max_site*2, smoothing* max_site)
y = np.sin(x)*.06
ax.plot(x,y+y_ax, linewidth = 3, solid_capstyle='round', color = color)
ax.plot(x[:smoothing*min_site],y[:smoothing*min_site]+y_ax, linewidth = 10, solid_capstyle='round', color = color)
#add data labels
ax.text(x[-1],y[-1]+y_ax + .1, max_site, size = 12, color= datalabels_color, ha = 'center')
ax.text(x[min_site*smoothing], y[min_site*smoothing]+y_ax+.1,min_site , size = 12, color= datalabels_color, ha = 'center', va = 'bottom')
ax.yaxis.set_ticks(y_axis, labels = reversed(countries),weight='bold')
ax.spines[['left', 'top','bottom','right']].set_visible(False)
ax.tick_params(axis='both', which='major', labelsize=12, length=0, color= xy_ticklabel_color)
ax.set_xticks([])
#add annotations
for site,year in zip(df.sites[0::3], df.year.unique()):
x = np.linspace(0, np.pi * site*2, smoothing* site)
ax.annotate(year, xy = (x.max(), max(y_axis)+.35), xytext=(x.max(), max(y_axis) + .85 ),
color='black', size = 12, ha='center', weight= "bold",
arrowprops=dict( arrowstyle='-',color = datalabels_color, ) ,
annotation_clip=False)
The result:

I would suggest using a sine, or cosine function to achieve the desired output instead of repeating arcs. In addition to making the figure look better, the number of lines the code should decrease as well.
I wish I could attach a figure, but here is what I am talking about.
x = np.linspace(0,np.pi*20, 1000)
y = np.sin(x)
plt.plot(x,y, linewidth = 3, solid_capstyle=’round’)
plt.plot(x[:700],y[:700], linewidth = 10, solid_capstyle=’round’)
plt.ylim(-30,30)
Let me know, if you think I should write the entire code for this one.
You are right, that would be more efficient!. Let me know if you re-write it otherwise I will do it 🙂
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
color_dict = {“Norway”: “#2B314D”, “Denmark”: “#A54836”, “Sweden”: “#5375D4″, }
xy_ticklabel_color, xy_label_color, grid_color, datalabels_color =’#101628′,”#101628”, “#C8C9C9”, “#757C85”
data = {
“year”: [2004, 2022, 2004, 2022, 2004, 2022],
“countries” : [ “Denmark”, “Denmark”, “Norway”, “Norway”,”Sweden”, “Sweden”,],
“sites”: [4,10,5,8,13,15]
}
df= pd.DataFrame(data)
df = df.sort_values([ ‘year’,’sites’], ascending=False ).reset_index(drop=True)
df[‘ctry_code’] = df.countries.astype(str).str[:2].astype(str).str.upper()
df[‘year_lbl’] =”‘”+df[‘year’].astype(str).str[-2:].astype(str)
sort_order_dict = {“Denmark”:2, “Sweden”:3, “Norway”:1, 2004:4, 2022:5}
df = df.sort_values(by=[‘year’,’countries’,], key=lambda x: x.map(sort_order_dict))
#map the colors of a dict to a dataframe
df[‘color’]= df.countries.map(color_dict)
max_sites = df[df.year == df.year.max()][‘sites’].to_list()
min_sites = df[df.year == df.year.min()][‘sites’].to_list()
colors = df.color.unique()
countries = df[‘ctry_code’].unique()
y_axis= [0,1,2]
fig, ax = plt.subplots(figsize=(6,6),sharex=True, sharey=True, facecolor = “#FFFFFF”, zorder= 1)
smoothing = 100
for y_ax, max_site, min_site,color in zip(reversed(y_axis), max_sites,min_sites,colors):
x = np.linspace(0, np.pi * max_site, smoothing* max_site)
y = np.sin(x)*.06
ax.plot(x,y+y_ax, linewidth = 3, solid_capstyle=’round’, color = color)
ax.plot(x[:smoothing*min_site],y[:smoothing*min_site]+y_ax, linewidth = 10, solid_capstyle=’round’, color = color)
#add data labels
ax.text(x[-1],y[-1]+y_ax + .1, max_site, size = 12, color= datalabels_color, ha = ‘center’)
ax.text(x[min_site*smoothing], y[min_site*smoothing]+y_ax+.1,min_site , size = 12, color= datalabels_color, ha = ‘center’, va = ‘bottom’)
ax.yaxis.set_ticks(y_axis, labels = reversed(countries),weight=’bold’)
ax.spines[[‘left’, ‘top’,’bottom’,’right’]].set_visible(False)
ax.tick_params(axis=’both’, which=’major’, labelsize=12, length=0, color= xy_ticklabel_color)
ax.set(xlim=[-1, (max(max_sites)+1)*np.pi], ylim=[ min(y_axis)-1, max(y_axis) + 1])
ax.set_xticks([])
#add annotations
ax.annotate(df.year.min(), xy = (min_sites[0]*np.pi, max(y_axis)+.25), xytext=(min_sites[0]*np.pi-0.85, max(y_axis) + .75 ),
color=’black’, size = 12, weight = “bold”,
arrowprops=dict( arrowstyle=’-‘,color = xy_label_color ) ,
annotation_clip=False)
ax.annotate(df.year.max(), xy = (max_sites[0]*np.pi, max(y_axis) +.25), xytext=(max_sites[0]*np.pi-0.85, max(y_axis) + .75),
color=’black’, size= 12, weight = “bold”,
arrowprops=dict( arrowstyle=’-‘,color = xy_label_color ) ,
annotation_clip=False)
Now it looks exactly the same, thanks for the feedback!