Need help to dynamically access to colomns in function!

Hello. I have table classif with columns:
... , group1, group2, group3, ... , group48, ...

In function i do query and want run on every row and dynamically operate on columns from group1 to group20. I do something like this:

OPEN curs FOR select * from classif;
 loop
    fetch curs into tmprec;
    exit when not found;
   
    for I in 1..20 loop
        ...
    -- problem code is:
        value := tmprec.group{I}; 
    -- i cannot dynamically access to group1, group2, ... colomns according to "I" variable.
    ...   

    end loop;
end loop;

I have to manually identify and handle each entry without a cycle do something like this:
value := tmprec.group1;
...
value := tmprec.group2;
...
value := tmprec.group2;
...
value := tmprec.group20;
   
Please help me to do it dynamically with a loop, depending on the I?
something like this in a loop:
value := tmprec.group{I}; 

Thanks.