Simplified Common Lisp reference

Symbol class: Conses, Lists and related functions

Syntax:

Symbol type: function

unionlist-1list-2key^(keyword)test^(keyword)test-not^(keyword) => list

Argument description:

list-1	list to be joined
list-2	other list to be joined
key	function for extracting value before test
test	function for comparison of two values
test-not	function for comparison of two values

UNION function computes union of two lists. Resulting list contains elements that appear in one or other list. See INTERSECTION, SET-DIFFERENCE, SET-EXCLUSIVE-OR.

(union '(1 2 3) '(2 3 4)) => (1 2 3 4)
(union '((1) (2) (3)) '((2) (3) (4))) => ((3) (2) (1) (2) (3) (4))
(union '((1) (2) (3)) '((2) (3) (4)) :test #'equal) => ((1) (2) (3) (4))
(union '((1) (2) (3)) '((2) (3) (4)) :key #'first) => ((1) (2) (3) (4))

Function index Full documentation for union (HyperSpec)