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.
'WASH' ∪ 'SHOUT' WASHOUT 'ONE' 'TWO' ∪ 'TWO' 'THREE' ONE TWO THREE
For performance information, see Search Functions and Hash Tables.