How to calculate percent by row and annotate 100 percent stacked bars

Question

I need help adding the percent distribution of the total (no decimals) in each section of a stacked bar plot in pandas created from a crosstab in a dataframe.

Here is sample data:

data = {
    'Name':['Alisa','Bobby','Bobby','Alisa','Bobby','Alisa',
            'Alisa','Bobby','Bobby','Alisa','Bobby','Alisa'],
    'Exam':['Semester 1','Semester 1','Semester 1','Semester 1','Semester 1','Semester 1',
            'Semester 2','Semester 2','Semester 2','Semester 2','Semester 2','Semester 2'],
     
    'Subject':['Mathematics','Mathematics','English','English','Science','Science',
               'Mathematics','Mathematics','English','English','Science','Science'],
   'Result':['Pass','Pass','Fail','Pass','Fail','Pass','Pass','Fail','Fail','Pass','Pass','Fail']}
df = pd.DataFrame(data)

# display(df)
     Name        Exam      Subject Result
0   Alisa  Semester 1  Mathematics   Pass
1   Bobby  Semester 1  Mathematics   Pass
2   Bobby  Semester 1      English   Fail
3   Alisa  Semester 1      English   Pass
4   Bobby  Semester 1      Science   Fail
5   Alisa  Semester 1      Science   Pass
6   Alisa  Semester 2  Mathematics   Pass
7   Bobby  Semester 2  Mathematics   Fail
8   Bobby  Semester 2      English   Fail
9   Alisa  Semester 2      English   Pass
10  Bobby  Semester 2      Science   Pass
11  Alisa  Semester 2      Science   Fail

Here is my code:

#crosstab
pal = ["royalblue", "dodgerblue", "lightskyblue", "lightblue"]
ax= pd.crosstab(df['Name'], df['Subject']).apply(lambda r: r/r.sum()*100, axis=1)
ax.plot.bar(figsize=(10,10),stacked=True, rot=0, color=pal)
display(ax)
    
plt.legend(loc='best', bbox_to_anchor=(0.1, 1.0),title="Subject",)

plt.xlabel('Name')
plt.ylabel('Percent Distribution')

plt.show()

I know I need to add a plt.text some how, but can’t figure it out. I would like the percent of the totals to be embedded within the stacked bars.

Asked By: Marie10

||

Source

Answer 1

Let’s try:

# crosstab
pal = ["royalblue", "dodgerblue", "lightskyblue", "lightblue"]
ax= pd.crosstab(df['Name'], df['Subject']).apply(lambda r: r/r.sum()*100, axis=1)
ax_1 = ax.plot.bar(figsize=(10,10), stacked=True, rot=0, color=pal)
display(ax)

plt.legend(loc='upper center', bbox_to_anchor=(0.1, 1.0), title="Subject")

plt.xlabel('Name')
plt.ylabel('Percent Distribution')

for rec in ax_1.patches:
    height = rec.get_height()
    ax_1.text(rec.get_x() + rec.get_width() / 2, 
              rec.get_y() + height / 2,
              "{:.0f}%".format(height),
              ha='center', 
              va='bottom')
    
plt.show()

Output:


Subject English Mathematics Science
Name            
Alisa   33.333333   33.333333   33.333333
Bobby   33.333333   33.333333   33.333333

Answered By: Scott Boston

Answer 2

From matplotlib 3.4.2 use matplotlib.pyplot.bar_label
- See this answer for a thorough explanation of using the method, and for additional examples.
- Using label_type='center' will annotate with the value of each segment, and label_type='edge' will annotate with the cumulative sum of the segments.
It is easiest to plot stacked bars using pandas.DataFrame.plot with kind='bar' and stacked=True
To get the percent in a vectorized manner (without .apply):
1. Get the frequency count using pd.crosstab
2. Divide ct along axis=0 by ct.sum(axis=1)
  - It is important to specify the correct axis with .div and .sum.
3. Multiply by 100, and round.
- This is best done using .crosstab because it results in a dataframe with the correct shape for plotting the stacked bars. .groupby would require further reshaping of the dataframe.
Tested in python 3.10, pandas 1.3.4, matplotlib 3.5.0

import pandas as pd
import matplotlib.pyplot as plt

# calculate the normalize value by row
ct = pd.crosstab(df['Name'], df['Subject'], normalize='index').mul(100).round(2)

# specify custom colors
pal = ["royalblue", "dodgerblue", "lightskyblue", "lightblue"]

# plot
ax = ct.plot(kind='bar', figsize=(10, 10), stacked=True, rot=0, color=pal, xlabel='Name', ylabel='Percent Distribution')

# move the legend
ax.legend(title='Subject', bbox_to_anchor=(1, 1.02), loc='upper left')

# iterate through each bar container
for c in ax.containers:

    # add the annotations
    ax.bar_label(c, fmt='%0.0f%%', label_type='center')

plt.show()

Using label_type='edge' annotates with the cumulative sum

`ct`

Subject  English  Mathematics  Science
Name                                  
Alisa      33.33        33.33    33.33
Bobby      33.33        33.33    33.33

Answered By: Trenton McKinney

How to calculate percent by row and annotate 100 percent stacked bars

Question:

Answers:

`ct`