在 Pandas 数据框中创建条件列

Question

I would like to create a calculated column which is as shown in line 1 but is 0 otherwise

 openOptions['Cash Reserve'] =  (openOptions['Quantity'] * openOptions['Strike'] * 100)
 openOptions['Cash Reserve'] = 0 if (openOptions['OptionType'] == 'C') else openOptions['Cash Reserve']

I get an error:

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

How should I resolve this?

Answer 1

You can use np.where() , which is like an if-then-else statement for numpy/Pandas, as follows:

openOptions['Cash Reserve'] = np.where(openOptions['OptionType'] == 'C',
                                       0,
                                       openOptions['Cash Reserve'])

Alternatively, as your Cash Reserve column has already been set up and you modify it to 0 only under a condition, you can also use .loc[] :

openOptions.loc[openOptions['OptionType'] == 'C', 'Cash Reserve'] = 0

Or even further simplified, as follows:

openOptions['Cash Reserve'][openOptions['OptionType'] == 'C'] = 0