how to get unique array from a 3 dimensional array based on two elements

I have requirement that when I retrieve listiems from a SharePoint online list I need to build another array of uniques combined elements.

I am retrieving list items fields of :

                                                ID,

                                                Service Unit,

                                                Category

Then I write each list item to an array. I need my final result to be an array where combination of Service Unit and Category is unique.

How can I accomplish that please?

faye fouladi