Where can I find the Top N Filter explained in this old trhead?
Based on that thread, they are refering to the jasperserver proffesional version.
It is where you can do ad hoc reporting and create you own calculation/formulas.
This is not available in the jasperstudio.
In the studio there are mutiple ways of doing this, depending on where you want to do it.
You can do it in the sql, you can sort the data etc.
You can also write you own java class and include the jar to your studio as a external jar.
Then you can call you class almost anywhere, pass the list to be sorted and return a sorted list.
Hope it clears up the confusion.