如何用Matplotlib为箱线图背景填充分层颜色？

问题说明 #

现有一段用Seaborn绘制铅含量按站点分布的箱线图代码，希望参考R绘制的带分层颜色背景的箱线图，为当前箱线图的Y轴方向添加分层背景色，尝试plt.fill_between未成功，寻求解决办法。

原代码：

# Importing necessary libraries
import matplotlib.pyplot as plt
import seaborn as sns


# Size of the plot in inches
plt.figure(figsize=(11, 6))

# Boxplot of the data
ax = sns.boxplot(x="CÓD. ESTAÇÃO", y="CHUMBO", data=df, linewidth=1, palette='Blues')

# Adjusting the y-axis range
ax.set_ylim(min(df['CHUMBO']) - 0.01, max(df['CHUMBO']) + 0.01)

# Adding title to the plot
plt.title("Boxplot of lead content by station", loc="center", fontsize=18)
plt.xlabel("Station Codes")
plt.ylabel("Lead Content")
ax.set_ylim(0, 0.045)

# Displaying the plot
plt.show()

解决方案 #

使用Matplotlib的ax.axhspan()函数绘制水平背景色块，该函数专门用于创建Y轴方向的水平跨度填充，比fill_between更适配这种分层背景需求。

修改后的代码 #

# Importing necessary libraries
import matplotlib.pyplot as plt
import seaborn as sns

# Size of the plot in inches
plt.figure(figsize=(11, 6))
ax = plt.gca()  # 获取当前坐标轴对象

# 绘制Y轴分层背景色（顺序从下到上，zorder设为0确保在箱线图下方）
# 分层区间和颜色可根据需求调整
ax.axhspan(0, 0.01, facecolor='#E8F4F8', zorder=0)
ax.axhspan(0.01, 0.02, facecolor='#C6E4EF', zorder=0)
ax.axhspan(0.02, 0.03, facecolor='#9DCBE3', zorder=0)
ax.axhspan(0.03, 0.045, facecolor='#73AFD8', zorder=0)

# 绘制箱线图，zorder=1确保在背景上方
ax = sns.boxplot(x="CÓD. ESTAÇÃO", y="CHUMBO", data=df, linewidth=1, palette='Blues', zorder=1)

# 设置Y轴范围
ax.set_ylim(0, 0.045)

# 添加标题与坐标轴标签
plt.title("Boxplot of lead content by station", loc="center", fontsize=18)
plt.xlabel("Station Codes")
plt.ylabel("Lead Content")

# 显示图表
plt.show()

关键说明 #

• ax.axhspan(y_min, y_max, facecolor=颜色, zorder=层级)：指定Y轴起止区间并填充对应颜色，zorder=0让背景处于最底层，箱线图设置zorder=1确保显示在背景之上。
• 分层区间和颜色可根据实际需求修改，比如参考R图的层级划分调整数值和配色。
• 先绘制背景再绘制箱线图，避免背景覆盖图表元素。

内容的提问来源于stack exchange，提问作者gongmaodu