Emacs Lisp: Remove Elements in List

remq

(remq x list)

• Remove all x in list.
• Returns a new list.
• The original list is unchanged.
• Comparison is done with eq. [see Emacs Lisp: Test Equality]

(setq xx '(3 4 5))
(remq 4 xx) ; (3 5)
xx ; (3 4 5)

delq

(delq x list)

• Remove all x in list.
• The original list is destroyed.
• Returns a new list.
• Comparison is done with eq. [see Emacs Lisp: Test Equality]

(setq xx '(3 4 5))

;; always set result to the same var
(setq xx (delq 4 xx)) ; (3 5)

Delete Duplicates

delete-dups

(delete-dups list)

This function destructively removes all duplicates from list, return a new list. The first one is kept among duplicates. Comparison done using equal. [see Emacs Lisp: Test Equality]

(setq xx '(3 4 5 3 2))
(setq xx (delete-dups xx)) ; (3 4 5 2)

Reference

• Lists (ELISP Manual)