Y must be a vector.  X must be a vector.  If either argument is a scalar, it is treated as a one-element vector.  R is a vector of the elements of X catenated with the elements of Y which are not found in X.

Items in X and Y are considered the same if X≡Y returns 1 for those items.

⎕CT and ⎕DCT are implicit arguments of Union.

Examples

      'WASH' ∪ 'SHOUT'
WASHOUT
 
      'ONE' 'TWO' ∪ 'TWO' 'THREE'
 ONE  TWO  THREE

For performance information, see Search Functions and Hash Tables.