cast only some columns

[pseudo oduesp]

Hi ,
 with fillna we can select  some columns to perform replace some values
 with chosing columns with dict
{columns :values }
but how i can  do  same with cast i have data frame with 300 columns and i
want just cats 4 from list columns  but with select query like that :

df.select(columns1.cast(int),columns2.cast(int),columns3.cast(int))

but i loose other columns
how i can performe on some columns without loosing other ones ?

thanks