Displaying unique value in dropdown

When I read "unique" my first thought is the union() function.  I'm not sure where you're dropdown values come from or how your objects are configured, but you could try something like below...

a!localVariables(
  
  local!selectedType,
  local!selectedCourse,
  local!dropdownOptionsMap: {
    a!map(course: "Java", type: "Premium"),
    a!map(course: "C++", type: "Premium"),
    a!map(course: "Appian", type: "Premium"),
    a!map(course: "Java", type: "Free"),
    a!map(course: "Python", type: "Free"),
    a!map(course: "Javascript", type: "Free"),
  },
  
  local!allCourseOptions: union(local!dropdownOptionsMap.course,local!dropdownOptionsMap.course),
  
  local!courseOptions: if(
    a!isNotNullOrEmpty(local!selectedType),
    index(local!dropdownOptionsMap, wherecontains(local!selectedType, local!dropdownOptionsMap.type)).course,
    local!allCourseOptions
  ),
  
  
  {
    a!dropdownField(
      label: "Course Type",
      placeholder: "Select Course Type",
      choiceLabels: union(local!dropdownOptionsMap.type,local!dropdownOptionsMap.type),
      choiceValues: union(local!dropdownOptionsMap.type,local!dropdownOptionsMap.type),
      value: local!selectedType,
      saveInto: {
        local!selectedType,
        a!save(local!selectedCourse, null)
      }
    ),
    a!dropdownField(
      label: "Course",
      placeholder: "Select Course",
      choiceLabels: local!courseOptions,
      choiceValues: local!courseOptions,
      value: local!selectedCourse,
      saveInto: {
        local!selectedCourse,
        a!save(
          local!selectedType,
          if(
            and(
              a!isNotNullOrEmpty(save!value),
              length(
                index(
                  local!dropdownOptionsMap,
                  wherecontains(
                    save!value,
                    local!dropdownOptionsMap.course
                  )
                ).type
              ) = 1
            ),
            index(
              local!dropdownOptionsMap,
              wherecontains(
                save!value,
                local!dropdownOptionsMap.course
              )
            ).type,
            null
          )
        )
      }
    )
  }
)

The list of course options begins with all unique values in the local!dropdownOptionsMap.course.  Notice Java is listed twice in local!dropdownOptionsMap.course.  To get the unique list I just used union(local!dropdownOptionsMap.course, local!dropdownOptionsMap.course).

Added some logic in course selection to set the type if the selected course is unique in the list of options and logic in the type selection to clear away any previously selected course.

Hope this helps!

Will try this.Thanks.

Will try this.Thanks.