python matplotlib如何将图例放在图外

关于matplotlib如何设置图例的位置？如何将图例放在图外？以及如何在一幅图有多个子图的情况下，删除重复的图例？我用一个简单的例子说明一下。

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure(1)
ax1 = fig.add_subplot(2,2,1)
ax2 = fig.add_subplot(2,2,2)
ax3 = fig.add_subplot(2,2,3)
ax4 = fig.add_subplot(2,2,4)

df1 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df2 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df3 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df4 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])



df1.plot(ax = ax1, title = "df1", grid = 'on')
df2.plot(ax = ax2, title = "df1", grid = 'on')
df3.plot(ax = ax3, title = "df1", grid = 'on')
df4.plot(ax = ax4, title = "df1", grid = 'on')

plt.show()

运行结果如下

可以看出，随机生成了几个dataframe,在一个figure()中生成了四个子图，每个子图的图例都是dataframe.columns里的值，那么如何移除这些图例？

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure(1)
ax1 = fig.add_subplot(2,2,1)
ax2 = fig.add_subplot(2,2,2)
ax3 = fig.add_subplot(2,2,3)
ax4 = fig.add_subplot(2,2,4)

df1 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df2 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df3 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df4 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])



df1.plot(ax = ax1, title = "df1", grid = 'on')
df2.plot(ax = ax2, title = "df1", grid = 'on')
df3.plot(ax = ax3, title = "df1", grid = 'on')
df4.plot(ax = ax4, title = "df1", grid = 'on')

ax1.legend_.remove()        ##移除子图ax1中的图例
ax2.legend_.remove()        ##移除子图ax2中的图例
ax3.legend_.remove()        ##移除子图ax3中的图例


plt.show()

可以看出ax1,ax2,ax3中的图例都被移除了，但是上图还不是很美观？有没有什么办法将图例放到图外面呢？请看:

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure(1)
ax1 = fig.add_subplot(2,2,1)
ax2 = fig.add_subplot(2,2,2)
ax3 = fig.add_subplot(2,2,3)
ax4 = fig.add_subplot(2,2,4)

df1 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df2 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df3 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])
df4 = pd.DataFrame(np.random.randn(3,5),columns = ['one','two','three','four','five'])



df1.plot(ax = ax1, title = "df1", grid = 'on')
df2.plot(ax = ax2, title = "df1", grid = 'on')
df3.plot(ax = ax3, title = "df1", grid = 'on')
df4.plot(ax = ax4, title = "df1", grid = 'on')

ax1.legend_.remove()
ax2.legend_.remove()
ax3.legend_.remove()
ax4.legend(loc=2, bbox_to_anchor=(1.05,1.0),borderaxespad = 0.)     ##设置ax4中legend的位置，将其放在图外

plt.show()

其中参数loc用于设置legend的位置
bbox_to_anchor用于在bbox_transform坐标（默认轴坐标）中为图例指定任意位置。

关于plt.legend更多的参数信息，详细见官方文档：http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.legend
关于legend的官方教程：详细见：http://matplotlib.org/users/legend_guide.html
关于pandas.DataFrame.plot更多的作图问题，详细见：http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.plot.html