About Expression Rule Functions

Use symmetricdifference() function.

a!localVariables(
  local!a: {1,2,3,4,5},
  local!b: {1,2,6,7,8},
  symmetricdifference(local!a,local!b)
)

O/P:

List of Number (Integer) - 6 items

• 3(Number (Integer))
• 4(Number (Integer))
• 5(Number (Integer))
• 6(Number (Integer))
• 7(Number (Integer))
• 8(Number (Integer))

Thank you for your reply.
However, because there are many fields in the CDT, it would be difficult to write an array.Is there any other way to achieve this without using an array?
For example, how to use the type! function to call the CDT and extract fields that are not duplicates.

you can use a!keys function to achieve your requirement. https://docs.appian.com/suite/help/22.4/fnc_informational_a_keys.html

1. First you need to get the CDT fileds form your CDT using keys function

2. Do a for each on your data and Index the  data using your keys 

3. Lastly compare the return data that you get form above step

Thanks, it looks like you can achieve your requirement that way.
However, I understand step 1, but I don't understand what kind of expression to write for steps 2 and 3.
If possible, can you show me a simple code sample?

Here is the sample example. Not sure exactly how your 3 CDTs looks like, consider this is an example

a!localVariables(
  local!cdt1: {
    a!map(c1v1: 1, c1v2: 2, c1v3: 3)
  },
  local!cdt2: {
    a!map(c2v1: 1, c2v2: 4, c2v3: 5)
  },
  local!cdt3: {
    a!map(c3v1: 6, c3v2: 2, c3v3: 7)
  },
  
  local!values: tointeger(
    a!forEach(
      items: {local!cdt1, local!cdt2, local!cdt3},
      expression: a!localVariables(
        local!keys: a!keys(fv!item),
        index(fv!item, local!keys, {})
      )
    )
  ),
  local!finalValues: reject(
    fn!isnull,
    tointeger(
      a!forEach(
        items: local!values,
        expression: if(
          length(wherecontains(fv!item, local!values)) > 1,
          null,
          fv!item
        )
      )
    )
  ),
  local!finalValues
)

You need to use nesting of symmetricdifference() function at multiple levels, depending on the number of fields you want to compare.

symmetricdifference(
    symmetricdifference(
        symmetricdifference(local!cdt1.field1,local!cdt2.field1).field2,
        symmetricdifference(local!cdt1.field1,local!cdt2.field1).field2
    ).field3,
    symmetricdifference(
        symmetricdifference(local!cdt1.field1,local!cdt2.field1).field2,
        symmetricdifference(local!cdt1.field1,local!cdt2.field1).field2
    ).field3
)