LISP - Symbols

Lisp - Set XOR

Quiz

Set XOR represents the elements which appears only once in both sets. Lisp provides set-exclusive-or, a built-in function to get the xor of two sets.

Syntax - set-exclusive-or function

(set-exclusive-or list1 list2 &key :test :test-not :key)

Arguments

list1− first set
list2− second set
:test− Function of two arguments to compare elements of Set. By default, eql is the function used.
:test-not− Function of two arguments returning true if elements are not equal.
:key− Function of one argument to be applied on each item of the set to be used for xor

Example - Set xor of sets of numbers

Following example shows the set xor of set of numbers.

main.lisp

; define a set of values
(defvar my-set-1 '(1 2 3 4 5 ))
; print the result
(print my-set-1)

(terpri)
; define another set of values
(defvar my-set-2 '(3 4 5 6 7))
; print the result
(print my-set-2)

(terpri)
; get set xor
(setf result-set (set-exclusive-or my-set-1 my-set-2))
; print the result
(print result-set)

Output

When you execute the code, it returns the following result −

(1 2 3 4 5) 
(3 4 5 6 7) 
(1 2 6 7)

Example - Set xor of sets of characters

Following example shows the set xor of set of characters.

main.lisp

; define a set of values
(defvar my-set-1 '(a b c d e))
; print the result
(print my-set-1)

(terpri)
; define another set of values
(defvar my-set-2 '(b c d e f g))
; print the result
(print my-set-2)

(terpri)
; get set xor
(setf result-set (set-exclusive-or my-set-1 my-set-2))
; print the result
(print result-set)

Output

When you execute the code, it returns the following result −

(A B C D E) 
(B C D E F G) 
(A F G)

Example - Set xor of sets of list using :test

Following example shows the set xor of set of list.

main.lisp

; define a set of lists
(defvar my-set-1 '((1 2)(3 4)))
; print the result
(print my-set-1)

(terpri)
; define another set of list
(defvar my-set-2 '((3 4)(5 6)))
; print the result
(print my-set-2)

(terpri)
; get set xor
(setf result-set (set-exclusive-or my-set-1 my-set-2 :test #'equal))
; print the result
(print result-set)

Output

When you execute the code, it returns the following result −

((1 2) (3 4)) 
((3 4) (5 6)) 
((1 2) (5 6))

Example - Set xor of sets of strings

Following example shows the set xor of set of strings.

main.lisp

; define a set of lists
(defvar my-set-1 '("apple" "banana" "cherry"))
; print the result
(print my-set-1)

(terpri)
; define another set of list
(defvar my-set-2 '("banana" "date"))
; print the result
(print my-set-2)

(terpri)
; get set xor
(setf result-set (set-exclusive-or my-set-1 my-set-2 :test #'string=))
; print the result
(print result-set)

Output

When you execute the code, it returns the following result −

("apple" "banana" "cherry") 
("banana" "date") 
("apple" "cherry" "date")

Key Considerations

set-exclusive-or is a non-destructive function. Original list is not modified and a new list is returned.
:test argument can be used to specify custom equality function.
:test-not argument is inverse of :test.
:key keyword allows to compare part of an element.

set-exclusive-or function is generally the most efficient and idiomatic way to perform set xor of Sets.

nset-exclusive-or, destructive version of set-exclusive-or

Lisp provides another version of set-exclusive-or function as nset-exclusive-or function. It may destroy the cells of first set.

Syntax - set-exclusive-or function

(set-exclusive-or list1 list2 &key :test :test-not :key)

Arguments

list1− first set
list2− second set
:test− Function of two arguments to compare elements of Set. By default, eql is the function used.
:test-not− Function of two arguments returning true if elements are not equal.
:key− Function of one argument to be applied on each item of the set to be used for xor

Example - Set xor of sets of numbers

Following example shows the set xor of set of numbers.

main.lisp

; define a set of values
(defvar my-set-1 '(1 2 3 4 5 ))
; print the result
(print my-set-1)

(terpri)
; define another set of values
(defvar my-set-2 '(3 4 5 6 7))
; print the result
(print my-set-2)

(terpri)
; get set xor
(setf result-set (nset-exclusive-or my-set-1 my-set-2))
; print the result
(print result-set)

Output

When you execute the code, it returns the following result −

(1 2 3 4 5) 
(3 4 5 6 7) 
(1 2 6 7)

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