How to annotate each segment of a stacked bar chart

I’ve been trying to annotate each sub-amount of a stacked bar chart with its values like the picture shown above (values not accurate, just an example).

df.iloc[1:].T.plot(kind='bar', stacked=True)
plt.show()

Data frame that I used:

The linked post is somewhat similar to my question but I do not understand the code given in that answer nor were there any explanations given.

Annotating Values in Stacked Bar Chart Matplotlib

Answer

Imports and DataFrame

import pandas as pd
import matplotlib.pyplot as plt

data = {'var': ['TR', 'AC', 'F&B'], '2019 1Q': [6600, 1256, 588], '2019 2Q': [6566, 1309, 586], '2019 3Q': [7383, 1525, 673]}
df = pd.DataFrame(data)
df.set_index('var', inplace=True)

# display(df)
     2019 1Q  2019 2Q  2019 3Q
var                           
TR      6600     6566     7383
AC      1256     1309     1525
F&B      588      586      673

Update as of matplotlib v3.4.2

• Use matplotlib.pyplot.bar_label
• See How to add value labels on a bar chart for additional details and examples with .bar_label.
• Tested with pandas v1.2.4, which is using matplotlib as the plot engine.

ax = df.T.plot.bar(stacked=True, figsize=(6, 5), rot=0)

for c in ax.containers:
    ax.bar_label(c, label_type='center')
    
ax.legend(title='Categories', bbox_to_anchor=(1.05, 1), loc='upper left')

Original Answer – prior to matplotlib v3.4.2

• Transpose the dataframe and then use pandas.DataFrame.plot.bar with stacked=True.
• An ndarray is returned with one matplotlib.axes.Axes per column with subplots=True.
  • In the case of this figure, ax.patches contains 9 matplotlib.patches.Rectangle objects, one for each segment of each bar.
    • By using the associated methods for this object, the height, width, x, and y locations can be extracted, and used to annotate the rectangles.
• The difference this question has from How to annotate a stacked bar chart with word count and column name? is the other question needs to extract and use alternate text for labels, and this dataframe needed to be transposed.

ax = df.T.plot.bar(stacked=True)
plt.legend(title='Categories', bbox_to_anchor=(1.05, 1), loc='upper left')

for i, rect in enumerate(ax.patches):
    # Find where everything is located
    height = rect.get_height()
    width = rect.get_width()
    x = rect.get_x()
    y = rect.get_y()

    # The height of the bar is the count value and can used as the label
    label_text = f'{height:.0f}'

    label_x = x + width / 2
    label_y = y + height / 2

    # don't include label if it's equivalently 0
    if height > 0.001:
        ax.text(label_x, label_y, label_text, ha='center', va='center', fontsize=8)