Question

I have 2 lists, I need to add the elements contained in the first list to the second list.
If the second list contain some of the element of the first list, those shoudn’t be added to the second list (to avoid repetitions).

At the moment I’m using:

set ListB to ListB & ListA

But obviously these doesn’t take into account duplicates.

Answer 1

When the list contains only strings and doesn’t contain linefeed as in adayzdone example code you can use a faster method when both lists contains thousands of items.

--NOTE: Only works with lists containing strings and not containing linefeeds. 
set listA to {"A1", "A2", "A3"}
set listB to {"B1", "B2", "A3"}

set AppleScript's text item delimiters to linefeed
set newList to every paragraph of (do shell script "sort -fu <<< " & quoted form of ((listA as string) & linefeed & listB as string))
set AppleScript's text item delimiters to ""

return newList