How to sort alphabetical order in attribute showing unique data of each column

[j00n162]

Hello,

While I was looking at the code that the author created, I had a curious if there is a way to sort the attribute showing unique data of each column in alphabetical order when the csv format converted to arff format. For example, in @Attribute 'Group', it shows {'h','f','b','a','c','d','e','g'}. But, I am wondering how I can make it show as {'a','b','c','d','e','f','g','h'}.

I've tried sort() function in the code, but it did not work and was confused about where to put it.
Please help me to solve this issue.

Thank you!