SQL & PL/SQL

I am trying to use a comma delimited string of numbers inside a 'where in' clause like this.

stringOfNumbers := '2, 21';

select *
from table
where id in (stringOfNumbers);

This of course becomes

select *
from table
where id in ('1,21');

As you can see this does not work.

Both (1,21) and ('1','21') works, but my problem is how to convert a comma delimited string into one of those formats?

The comma delimited string is actually made like this inside a loop:

stringOfNumber := v_idsMatch || v_resdata.res_id || ''',''';

(I do another step trimming the string for the extra ',' at the end).

Any advice?

Regards
Runski