如何在matplotlib中的条形图中添加多个数据标签

Question

我有两组条形图，显示了 3 组中两个系统的案例之间的值变化，如下所示。在这里，我可以使用下面的代码向条形图添加数据标签（附上生成的图）

我想要做的是在顶部（或值案例中的负变化的底部），添加一个额外的数据标签来捕获值变化的百分比，如第二张图所示，其中 33% 为红色（我手动编辑了它）。我如何从这段代码中实现这一点？提前谢谢你。

import matplotlib.pyplot as plt
import numpy as np

value_case0_system1 = np.array([30, 20, 40])
value_case1_system1 = np.array([20, 25, 50])
value_case2_system1 = np.array([10, 35, 45])

value_case1_system2 = np.array([60, 50, 40])
value_case2_system2 = np.array([50, 40, 55])

change_case0_to_case1_system1 = np.subtract(value_case1_system1,value_case0_system1)
change_case1_to_case2_system1 = np.subtract(value_case2_system1,value_case1_system1)
change_case1_to_case2_system2 = np.subtract(value_case2_system2,value_case1_system2)

fig, (ax0, ax1) = plt.subplots(nrows=1, ncols=2, sharey=True, figsize=(18,10))
labels = ['Group 1', 'Group 2', 'Group 3']
x = np.arange(len(labels))
ax0.set_ylabel('Change in Values', va='center', rotation='vertical',
         fontsize=17, fontweight='bold')
width = 0.28
ax0.set_title('System 1', fontsize=17, fontweight='bold')
ax0.axhline(y=0, color='black', ls=':', lw=2)
ax0.set_xticks(x)
ax0.set_xticklabels(labels,fontsize=15)
rects1 = ax0.bar(x-width/2, change_case0_to_case1_system1, width, label='Case 0 to Case 1',
        color='#292929', edgecolor='black', linewidth=1)
rects2 = ax0.bar(x+width/2, change_case1_to_case2_system1, width, label='Case 1 to Case 2',
        color='#7f6d5f', edgecolor='black', linewidth=1)
ax0.bar_label(rects1, padding=3, fontsize=11)
ax0.bar_label(rects2, padding=3, fontsize=11)
leg = ax0.legend(loc="upper left", bbox_to_anchor=[0, 1],
                 ncol=1, fancybox=True)
ax0.legend(fontsize=15)

ax1.set_title('System 2', fontsize=17, fontweight='bold')
ax1.axhline(y=0, color='black', ls=':', lw=2)
ax1.set_xticks(x)
ax1.set_xticklabels(labels,fontsize=15)

rects3 = ax1.bar(x, change_case1_to_case2_system2, width, label='Case 1 to Case 2',
        color='#7f6d5f', edgecolor='black', linewidth=1)
ax1.legend(shadow=True, fancybox=True)
ax1.bar_label(rects3, padding=3, fontsize=11)
leg = ax1.legend(loc="upper left", bbox_to_anchor=[0, 1],
                 ncol=1, fancybox=True)
ax1.legend(fontsize=15)
plt.tight_layout()
plt.show()

Answer 1

额外绘图格式的代码已被省略，因为它与答案无关。可以根据您的要求加回去。
每个 .bar_label colors the label globally, so unlike this ，需要添加第二个 .bar_label 用于百分比变化，具有不同的 color 和 padding
对于每个个案，计算百分比变化，并在列表理解中设置字符串格式。
- 将字符串格式计算列表设置为.bar_label中的labels参数。
给定 OP 中的代码，需要添加 6 行代码，3 行用于创建标签列表，3 行用于将标签添加到图中。
其他资源：
- matplotlib: Bar Label Demo
- Adding value labels on a matplotlib bar chart
在 python 3.8.11、matplotlib 3.4.3

change_case0_to_case1_system1 = np.subtract(value_case1_system1, value_case0_system1)
# add list of string formatted percent change calculation
per_change_case0_to_case1_system1 = [f'({v}%)' for v in (change_case0_to_case1_system1 / value_case0_system1).round(2)*100]

change_case1_to_case2_system1 = np.subtract(value_case2_system1, value_case1_system1)
# add list of string formatted percent change calculation
per_change_case1_to_case2_system1 = [f'({v}%)' for v in (change_case1_to_case2_system1 / value_case1_system1).round(2)*100]

change_case1_to_case2_system2 = np.subtract(value_case2_system2, value_case1_system2)
# add list of string formatted percent change calculation
per_case1_to_case2_system2 = [f'({v}%)' for v in (change_case1_to_case2_system2 / value_case1_system2).round(2)*100]

fig, (ax0, ax1) = plt.subplots(nrows=1, ncols=2, sharey=True, figsize=(18,10))
labels = ['Group 1', 'Group 2', 'Group 3']
x = np.arange(len(labels))

width = 0.28

ax0.set_xticks(x)
ax0.set_xticklabels(labels, fontsize=15)

rects1 = ax0.bar(x-width/2, change_case0_to_case1_system1, width, label='Case 0 to Case 1', color='#292929', edgecolor='black', linewidth=1)
rects2 = ax0.bar(x+width/2, change_case1_to_case2_system1, width, label='Case 1 to Case 2', color='#7f6d5f', edgecolor='black', linewidth=1)

ax0.bar_label(rects1, padding=3, fontsize=11)
# add a second annotation with the string formatted labels
ax0.bar_label(rects1, labels=per_change_case0_to_case1_system1, padding=15, fontsize=11, color='red')

ax0.bar_label(rects2, padding=3, fontsize=11)
# add a second annotation with the string formatted labels
ax0.bar_label(rects2, labels=per_change_case1_to_case2_system1, padding=15, fontsize=11, color='red')

rects3 = ax1.bar(x, change_case1_to_case2_system2, width, label='Case 1 to Case 2', color='#7f6d5f', edgecolor='black', linewidth=1)

ax1.set_xticks(x)
ax1.set_xticklabels(labels,fontsize=15)

ax1.bar_label(rects3, padding=3, fontsize=11)
# add a second annotation with the string formatted labels
ax1.bar_label(rects3, labels=per_case1_to_case2_system2, padding=15, fontsize=11, color='red')

plt.tight_layout()
plt.show()

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