Emacs Lisp: Sequence Functions

Here's a collection of functions that works on Sequence type.

Note, this page does not include specialized functions for Association List nor Property List .

Convert/Join Sequence/List/Vector/String

• Emacs Lisp: Convert/Join Sequence/List/Vector/String

Sequence Functions

These functions work on any Sequence Type .

Those starting with “seq-” are new in emacs 25.1, released in 2016-09. They are from “seq.el”, and the file is loaded when emacs starts. You may want to explicitly declare (require 'seq).

Some of these provide new functionalities, some gives a unified interface to old functions.

• length
• sequencep
• elt
• copy-sequence
• reverse
• nreverse
• sort
• seq-elt
• seq-length
• seqp
• seq-drop
• seq-take
• seq-take-while
• seq-drop-while
• seq-do
• seq-map
• seq-mapn
• seq-filter
• seq-remove
• seq-reduce
• seq-some
• seq-find
• seq-every-p
• seq-empty-p
• seq-count
• seq-sort
• seq-contains
• seq-position
• seq-uniq
• seq-subseq
• seq-concatenate
• seq-mapcat
• seq-partition
• seq-intersection
• seq-difference
• seq-group-by
• seq-into
• seq-min
• seq-max
• seq-doseq
• seq-let

Check Existence

(member x list)

Check if x is in list. If so, return a list starting with the first occurrence of object. Else return nil. Comparison done using equal. [see Emacs Lisp: Test Equality]

(member "4" '("3" "4" "5")) ;; ("4" "5")

(member-ignore-case x list)

same as member, except that x should be a string, and comparison ignores letter-case.

(member-ignore-case "A" '("b" "a")) ; ("a")

(memq x list)

Same as member, but comparison done using eq. Use this if all items are Symbols.

(memql x list)

Same as member, but comparison done using eql.

Delete Elements

(delete x sequence)

• Remove all x in sequence.
• The original sequence is destroyed if it's a list.
• Returns a new sequence.
• Comparison is done with equal. [see Emacs Lisp: Test Equality]

(setq xx '(3 4 5))

;; always set result to the same var. because original is usually destroyed
(setq xx (delete 4 xx)) ; (3 5)

;; on vector
(setq xx [3 4 5])
(setq xx (delete 4 xx)) ; [3 5]

(delq x sequence)

Same as delete, except the comparison is done with eq. Use this if all items are Symbols.

(setq xx '(3 4 5))

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

(remove x sequence)

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

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

(remq x list)

Same as remove, except the comparison is done with eq.

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

Delete Duplicates

(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)

Misc

• nconc

Reference

• (info "(elisp) Sequence Functions")
• (info "(elisp) Sets And Lists")

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