Elisp: Vector

What is Vector

Emacs lisp vector datatype is a ordered sequence of values, with fixed number of elements. It implements the array data structure.

• Vector is a ordered sequence of values.
• Any element can be any type, mixed.
• Element's value can be changed.
• Number of elements cannot change. (i.e. Vector's length is fixed.)
• Read/Write to any position has constant access time.

Create Vector

make-vector

(make-vector length val)

Create a vector of given length and value for all elements.

(make-vector 3 0)
;; [0 0 0]

vector

(vector a b etc)

Create a vector with elements, the elements are evaluated.

 (let ((xx 3))
  (vector 1 2 xx))
;; [1 2 3]

[a b etc]

Create a vector, do not evaluate elements. Typically used when all elements are numbers or Symbols .

(setq xx [3 yy 5])
;; [3 yy 5]

(aref xx 1)
;; yy

(symbolp (aref xx 1))
;; t

Fill Vector

fillarray

(fillarray arrayVar val)

Make all elements of arrayVar to have value val, modify the arrayVar, return the variable's new value.

arrayVar can a variable of array, or just array. 〔see Elisp: Sequence Type〕

(setq xx [3 4 5])
;; [3 4 5]

(fillarray xx 1)
;; [1 1 1]

xx
;; [1 1 1]

(fillarray [3 4 5] 1)
;; [1 1 1]

Length

(length (vector 7 4 5))
;; 3

Get Element

aref

(aref array n)

Return the element of array at index n.

;; get a element from vector
(aref ["a" "b" "c"] 0)
;; "a"

Change Element

aset

(aset arrayVar idx new)

• Change element of arrayVar at index idx the value new.
• Modifies arrayVar.
• Return new.

(setq xx [3 4 5])
;; [3 4 5]

(aset xx 0 "b")
;; "b"

xx
;; ["b" 4 5]

Nested Vector

Vector can be nested in any way, because the elements can be any type.

;; nested vector
[[1 2] [3 4]] ; 2 by 2 matrix

;; random nested vector
[8 [3 [2 9] c] 7 [4 "b"]]

Reference

• Sequences Arrays Vectors (ELISP Manual)