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6.3 Functions that Operate on Arrays

In this section, we describe the functions that accept all types of arrays.

function arrayp object​

This function returns t if object is an array (i.e., a vector, a string, a bool-vector or a char-table).

(arrayp [a])
     ⇒ t
(arrayp "asdf")
     ⇒ t
(arrayp (syntax-table))    ;; A char-table.
     ⇒ t

function aref arr index​

This function returns the indexth element of the array or record arr. The first element is at index zero.

(setq primes [2 3 5 7 11 13])
     ⇒ [2 3 5 7 11 13]
(aref primes 4)
     ⇒ 11
(aref "abcdefg" 1)
     ⇒ 98           ; ‘b’ is ASCII code 98.

See also the function elt, in Sequence Functions.

function aset array index object​

This function sets the indexth element of array to be object. It returns object.

(setq w (vector 'foo 'bar 'baz))
     ⇒ [foo bar baz]
(aset w 0 'fu)
     ⇒ fu
w
     ⇒ [fu bar baz]
;; copy-sequence copies the string to be modified later.
(setq x (copy-sequence "asdfasfd"))
     ⇒ "asdfasfd"
(aset x 3 ?Z)
     ⇒ 90
x
     ⇒ "asdZasfd"

The array should be mutable. See Mutability.

If array is a string and object is not a character, a wrong-type-argument error results. The function converts a unibyte string to multibyte if necessary to insert a character.

function fillarray array object​

This function fills the array array with object, so that each element of array is object. It returns array.

(setq a (copy-sequence [a b c d e f g]))
     ⇒ [a b c d e f g]
(fillarray a 0)
     ⇒ [0 0 0 0 0 0 0]
a
     ⇒ [0 0 0 0 0 0 0]
(setq s (copy-sequence "When in the course"))
     ⇒ "When in the course"
(fillarray s ?-)
     ⇒ "------------------"

If array is a string and object is not a character, a wrong-type-argument error results.

The general sequence functions copy-sequence and length are often useful for objects known to be arrays. See Sequence Functions.