Python：制作一个跨越两个子图的图例

Question

我正在寻找的基本设计是我有两个并排的散点图，然后我想在两个子图下方创建一个图例，跨越它们。这是一个粗略的草图：

我能够使情节没有问题，但我很难让传奇人物做我想做的事。这是我制作两个散点图的代码示例（我有比这更多的数据点，但为了空间，我只包括一些）：

import numpy as np
from numpy import array
import matplotlib.pyplot as plt

x = [5,10,20,30]

med1 = [9.35,15.525,26.1,48.275]
med2 = [8.75,14.025,23.95,41.025] 

iqr1 = [13.5125,19.95,38.175,69.9] 
iqr2 = [12.05,19.075,35.075,62.875]

plt.subplot(121)
plt.scatter(x, med1, color='red', alpha=0.5, label='Red stuff')
plt.scatter(x, med2, color='blue', alpha=0.5, label='Blue stuff')
plt.xlim([0,35])
plt.ylim([0,75])
plt.xlabel('Channel Area')
plt.ylabel('Median')

plt.subplot(122)
plt.scatter(x, iqr1, color='red', alpha=0.5, label='More Red Stuff')
plt.scatter(x, iqr2, color='blue', alpha=0.5, label = 'More Blue Stuff')
plt.xlim([0,35])
plt.ylim([0,75])
plt.xlabel('Channel Area')
plt.ylabel('IQR')

使图例如上图所示的最佳方式是什么？

Answer 1

你想使用figlegend (demo)

figlegend( (line1, line2, line3), ('label1', 'label2', 'label3'), 'upper right' )

也看看这个问题的答案 How to position and align a matplotlib figure legend?

Answer 2

从matplotlib - Legend with multiple axes with errorbar object 和How to put the legend out of the plot 借用代码，您可以使用这些命令来做到这一点：

#获取lengend句柄和标签 h1, l1 = ax1.get_legend_handles_labels() h2, l2 = ax2.get_legend_handles_labels()

#Shrink the subplots to make room for the legend
box = ax1.get_position()
ax1.set_position([box.x0, box.y0 + box.height * 0.1,
                 box.width, box.height * 0.9])
box = ax2.get_position()
ax2.set_position([box.x0, box.y0 + box.height * 0.1,
                 box.width, box.height * 0.9])
#Make the legend
ax1.legend(h1+h2, l1+l2,  bbox_to_anchor=(0,-.05, 2.2,-0.15), loc=9,
           ncol=4)

其中 ax1 和 ax2 是子图的轴

在您的示例中，您可以这样实现：

import matplotlib.pyplot as plt
plt.style.use('ggplot')

x = [5,10,20,30]

med1 = [9.35,15.525,26.1,48.275]
med2 = [8.75,14.025,23.95,41.025] 

iqr1 = [13.5125,19.95,38.175,69.9] 
iqr2 = [12.05,19.075,35.075,62.875]

ax1 = plt.subplot(121)
plt.scatter(x, med1, marker='^',color='black', alpha=0.5, label='Triangle!')
plt.scatter(x, med2, color='blue', alpha=0.5, label='Blue Dot')
plt.xlim([0,35])
plt.ylim([0,75])
plt.xlabel('Channel Area')
plt.ylabel('Median')
# ax1 = plt.gca()

ax2 = plt.subplot(122)
plt.scatter(x, iqr1, color='red', alpha=0.5, label='Red Dot')
plt.scatter(x, iqr2, marker='D',color='blue', alpha=0.5, label = 'Diamonds')
plt.xlim([0,35])
plt.ylim([0,75])
plt.xlabel('Channel Area')
plt.ylabel('IQR')
# ax2=plt.gca()

plt.tight_layout() # No overlap of subplots

#Get the lengend handles and labels
h1, l1 = ax1.get_legend_handles_labels()
h2, l2 = ax2.get_legend_handles_labels()

#Shrink the subplots to make room for the legend
box = ax1.get_position()
ax1.set_position([box.x0, box.y0 + box.height * 0.1,
                 box.width, box.height * 0.9])
box = ax2.get_position()
ax2.set_position([box.x0, box.y0 + box.height * 0.1,
                 box.width, box.height * 0.9])
#Make the legend
ax1.legend(h1+h2, l1+l2,  bbox_to_anchor=(0,-.05, 2.2,-0.15), loc=9,
           ncol=4)
plt.show()

您可以使用bbox、ncol、mode="expand"、borderaxespad=0。有关更多信息，请参阅http://matplotlib.org/users/legend_guide.html#legend-location。上面的代码应该会产生这个情节：