How to display value if value is unique or duplicate in a column using an arrayformula Google sheets

I have a formula that returns either Unique or Duplicate depending on whether there already exists another value in the same column.

The formula =IF(COUNTIF($A$2:$A2,A2)=1, "Unique", "Duplicate") in B2

Example:

  A      B
Peter | Unique
James | Unique
Peter | Duplicate
Anne  | Unique
James | Duplicate

The formula works as it should but I am looking for an alternative formula that works with arrayformula()

The reason is because my data is dynamic which means the ranges change time and time again. It’s not possible to manually drag the current formula each time the ranges change so an arrayformula for this would be very welcome.

>Solution :

Use this to be able to specify the range in this case A2:A once in LAMBDA() call.

=ARRAYFORMULA(
 LAMBDA(r   ,IF(r="",,IF(XMATCH(r,r,0,1)=SEQUENCE(ROWS(r))<>TRUE,
       "Duplicate","Unique")))
       (A2:A))

Used formulas help
ARRAYFORMULA – LAMBDA – IF – SEQUENCE – ROWS – UNIQUE