extract unique values from list of strings

It looks like it's possible that there can be multiple values within a single text item - is that correct? Do you anticipate that it will always show with a semicolon separator if there are multiple values?

If you are confident in the format, you should be able to do this with several steps: (1) split each item by the semicolon (2) combine them all into a single list and (3) use the union() function to return a unique list of items. Something like this should work:

a!localVariables(
  local!data: {
    "user1",
    "user2",
    "user2; user3",
    "user4"
  },
  union(
    a!flatten(
      a!forEach(
        items: local!data,
        expression: trim(split(fv!item, ";"))
      )
    ),
    touniformstring({})
  )
)