TypeError：将第二个图例添加到绘图时，“PathCollection”对象不可迭代

Posted 2023-03-11

【中文标题】TypeError：将第二个图例添加到绘图时，“PathCollection”对象不可迭代

【英文标题】：TypeError: 'PathCollection' object is not iterable when adding second legend to plot

【发布时间】：2017-02-20 10:10:04

【问题描述】：

我正在从三个单独的数据框制作散点图，并绘制点以及最佳拟合线。我可以使用以下代码完成此操作：

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

fig=plt.figure()
ax1=fig.add_subplot(111)
ax2=fig.add_subplot(111)
ax3=fig.add_subplot(111)

#create scatter plots from the dataframes
ax1.scatter(ex_x, ex_y, s=10, c='r', label='Fire Exclusion')
ax2.scatter(one_x,one_y, c='b', marker='s',label='One Fire')
ax3.scatter(two_x, two_y, s=10, c='g', marker='^', label='Two Fires')

#plot lines of best fit
ax1.plot(ex_x,ex_results.predict(), color = 'r',label = 'Linear (Fire Exclusion)')
ax2.plot(one_x,one_results.predict(), color = 'b',label = 'Linear (One Fire)')
ax3.plot(two_x,two_results.predict(), color = 'g',label = 'Linear (Two Fires)')

#add legend and axis labels
plt.xlabel('NDVI 2004/07/27')
plt.ylabel('NDVI 2005/07/14')
plt.title('NDVI in 2004 vs. 2005')
plt.legend(loc='center left', bbox_to_anchor=(1, 0.5), scatterpoints=1)

这给了我：

现在我想添加第二个图例，它将显示每行的 r2。我正在尝试这样做：

fig=plt.figure()
ax1=fig.add_subplot(111)
ax2=fig.add_subplot(111)
ax3=fig.add_subplot(111)

scat1,=ax1.scatter(ex_x, ex_y, s=10, c='r', label='Fire Exclusion')
scat2,=ax2.scatter(one_x,one_y, c='b', marker='s',label='One Fire')
scat3,=ax3.scatter(two_x, two_y, s=10, c='g', marker='^', label='Two Fires')

lin1,=ax1.plot(ex_x,ex_results.predict(), color = 'r',label = 'Linear (Fire Exclusion)')
lin2,=ax2.plot(one_x,one_results.predict(), color = 'b',label = 'Linear (One Fire)')
lin3,=ax3.plot(two_x,two_results.predict(), color = 'g',label = 'Linear (Two Fires)')

l1 = plt.legend([scat1, scat2,scat3,lin1,lin2,lin3], ["Fire Exclusion", "One Fire", "Two Fires", "Linear (Fire Exclusion)", "Linear (One Fire)", "Linear (Two Fires)"], loc='upper left', scatterpoints=1)

#get r2 from regression results
r2ex=ex_results.rsquared
r2one=one_results.rsquared
r2two=two_results.rsquared

plt.legend([r2ex, r2one, r2two], ['R2 (Fire Exclusion)', 'R2 (One Fire)', 'R2 (Two Fires)'], loc='lower right')

plt.gca().add_artist(l1)
plt.xlabel('NDVI 2004/07/27')
plt.ylabel('NDVI 2005/07/14')
plt.title('NDVI in 2004 vs. 2005')

但这会返回：

Traceback (most recent call last):

  File "<ipython-input-32-b6277bf27ded>", line 1, in <module>
    runfile('E:/prelim_codes/Fire.py', wdir='E:/prelim_codes')

  File "C:\Users\Stefano\Anaconda2_2\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 714, in runfile
    execfile(filename, namespace)

  File "C:\Users\Stefano\Anaconda2_2\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 74, in execfile
    exec(compile(scripttext, filename, 'exec'), glob, loc)

  File "E:/prelim_codes/Fire.py", line 539, in <module>
    scat1,=ax1.scatter(ex_x, ex_y, s=10, c='r', label='Fire Exclusion')

TypeError: 'PathCollection' object is not iterable

【参考方案1】：

我有同样的错误。我发现你不应该在变量名之后包含逗号。所以试试

scat1 =ax1.scatter(ex_x, ex_y, s=10, c='r', label='Fire Exclusion')
scat2 =ax2.scatter(one_x,one_y, c='b', marker='s',label='One Fire')
scat3 =ax3.scatter(two_x, two_y, s=10, c='g', marker='^', label='Two Fires')

而不是

scat1,=ax1.scatter(ex_x, ex_y, s=10, c='r', label='Fire Exclusion')
scat2,=ax2.scatter(one_x,one_y, c='b', marker='s',label='One Fire')
scat3,=ax3.scatter(two_x, two_y, s=10, c='g', marker='^', label='Two Fires')

这是因为 axes.scatter 返回的 PathCollection 与 axes.plot 不同，它返回绘制线的元组（请参阅 http://matplotlib.org/1.3.1/users/pyplot_tutorial.html#controlling-line-properties 和 Python code. Is it comma operator?）。

因此，对于您的行，您仍然需要逗号，因为您正在解包元组，但对于散布，您不应该有逗号。

【讨论】：

天哪，非常感谢。我已经疯了 30 分钟，直到我看到你对那个 #$%@ 逗号的回答！