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.