pandas DataFrame set value on boolean mask

Question

I\'m trying to set a number of different in a pandas DataFrame all to the same value. I thought I understood boolean indexing for pandas, but I haven\'t found any resources

Answer 1

I'm not 100% sure but I suspect the error message relates to the fact that there is not identical treatment of missing data across different dtypes. Only float has NaN, but integers can be automatically converted to floats so it's not a problem there. But it appears mixing number dtypes and object dtypes does not work so easily...

Regardless of that, you could get around it pretty easily with np.where:

df[:] = np.where( mask, 30, df ) 

    A   B
0  30  30
1   2   b
2  30   f