Python/pandas idiom for if/then/else [duplicate]

Question

After performing calculations on an entire pandas dataframe, I need to go back and override variable calculations (often setting to zero) based on the value of another variable(s). Is there a more succinct/idiomatic way to perform this kind of operation?

df['var1000'][df['type']==7] = 0
df['var1001'][df['type']==7] = 0
df['var1002'][df['type']==7] = 0
...
df['var1099'][df['type']==7] = 0

Is there a pandas-y way to do something like this?

if (df['type']==7):
    df['var1000'] = 0
    df['var1001'] = 0
    df['var1002'] = 0
    ...
    df['var1099'] = 0

Answer 1

df.ix[df.type==7, ['var1001', 'var1002']] = 0

If you're doing it on all columns, you can just do df.ix[df.type==7] = 0. Or of course if you have a list of the columns whose values you want to replace, you can pass that list in the second slot:

columnsToReplace = ['var1001', 'var1002', ...]
df.ix[df.type==8, columnsToReplace] = 0