Mapping unique list to current dataset in Pentaho Javascript

Question

I need to generate an unique list of values and assign it dynamically in java script to each row of a data set. I understand that the way the Modified Javascript value works is by applying the same script to each row, so how can I generate a unique list of values (in javascript) and apply one value of the list to each row of the dataset. The unique list has to be generated only once; do I need to do it outside of a Modified Java Script Value?