pandas replace null values for a subset of columns

Question

I have a data frame with many columns, say:

df:
name   salary  age   title
John      100   35    eng
Bill      200  NaN    adm
Lena      NaN   28    NaN
Jane             


        

Answer 1

It is not so beautiful, but it works:

df.salary.fillna(-1, inplace=True)
df.age.fillna(-1, inplace=True)
df
>>>    name  salary   age title
    0  John   101.0  35.0   eng
    1  Bill   200.0  -1.0   adm
    2  Lena    -1.0  28.0   NaN
    3  Jane   120.0  45.0   eng