向 Pandas DataFrame 箱线图添加图例

Question

我正在同一轴上绘制一系列箱线图，并希望添加图例来识别它们。非常简化，我的脚本如下所示：

import pandas as pd
import matplotlib.pyplot as plt
import numpy as np
df={}
bp={}
positions = [1,2,3,4]
df[0]= pd.DataFrame (np.random.rand(4,4),columns =['A','B','C','D'])
df[1]= pd.DataFrame (np.random.rand(4,4),columns =['A','B','C','D'])
colour=['red','blue']
fig, ax = plt.subplots()
for i in [0,1]:
    bp[i] = df[i].plot.box(ax=ax,
                          positions = positions,
                          color={'whiskers': colour[i],
                                 'caps': colour[i],
                                 'medians': colour[i],
                                 'boxes': colour[i]}
                          )
plt.legend([bp[i] for i in [0,1]], ['first plot', 'second plot'])
fig.show()

情节很好，但图例没有绘制，我收到此警告

    UserWarning: Legend does not support <matplotlib.axes._subplots.AxesSubplot object at 0x000000000A7830F0> instances.
A proxy artist may be used instead.

（我之前在向散点图添加图例时收到过此警告，但图例仍然被绘制，所以我可以忽略它。）

这是 的描述的链接proxy artists，但不清楚如何将其应用到我的脚本中。有什么建议么？

Answer 1

'pandas' 绘制AxesSubplot不能用于生成图例的返回对象。您必须使用以下命令生成自己的图例proxy artist。我修改了你的代码：

import pandas as pd
import matplotlib.pyplot as plt
import numpy as np
import matplotlib.patches as mpatches
df={}
bp={}
positions = [1,2,3,4]
df[0]= pd.DataFrame (np.random.rand(4,4),columns =['A','B','C','D'])
df[1]= pd.DataFrame (np.random.rand(4,4),columns =['A','B','C','D'])
colour=['red','blue']
fig, ax = plt.subplots()
for i in [0,1]:
    bp[i] = df[i].plot.box(ax=ax,
                          positions = positions,
                          color={'whiskers': colour[i],
                                 'caps': colour[i],
                                 'medians': colour[i],
                                 'boxes': colour[i]}
                          )

red_patch = mpatches.Patch(color='red', label='The red data')
blue_patch = mpatches.Patch(color='blue', label='The blue data')
plt.legend(handles=[red_patch, blue_patch])

plt.show()

结果如下所示：