python - 难以创建 Pandas Dataframe 的列

Question

我想基于现有列创建数据框的新列，但我希望它以数据框中的另一个现有列为条件。以下代码不起作用。有谁知道为什么吗？

if CV['keyword'] == 0:
    CV['left out'] = (CV['Prediction Numerator'] - (CV['Rate'] *10000))/(CV['Prediction Denominator'] - 10000)
else:
    CV['left out'] = (CV['Prediction Numerator'] - (CV['Rate'] *10000 * 10))/(CV['Prediction Denominator'] - (10000 * 10))

我收到以下错误:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\bwei\Downloads\WinPython-64bit-2.7.9.4\python-2.7.9.amd64\lib\site-packages\pandas\core\generic.py", line 709, in __nonzero__
    .format(self.__class__.__name__))
ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

这是我的数据框前 ​​4 列的片段。

        Zip  keyword  Prediction Numerator  Prediction Denominator  
0     01001        0        7650546.693200            40002.558782   
1     01001        0        7650546.693200            40002.558782   
2     01001        0        7650546.693200            40002.558782   
3     01001        0        7650546.693200            40002.558782   
4     01002        0            157.951741                0.718621   
5     01002        0            157.951741                0.718621   
6     01005        0        3600150.148240            20000.671431   
7     01005        0        3600150.148240            20000.671431   
8     01007        0        6932235.816260            30000.936191   
9     01007        0        6932235.816260            30000.936191   
10    01007        0        6932235.816260            30000.936191   

谢谢，本

Answer 1

这应该有效:

CV.loc[CV['keyword']==0,'left out']=expression1
CV.loc[CV['keyword']!=0,'left out']=expression2