GNU Emacs Lisp Reference Manual

6.3: Functions that Operate on Arrays

In this section, we describe the functions that accept both strings and vectors.

Function: arrayp object

This function returns t if object is an array (i.e., either a vector or a string).

(arrayp [a])
=> t
(arrayp "asdf")
=> t

Function: aref array index

This function returns the indexth element of array. 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
(elt 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 [foo bar baz])
     => [foo bar baz]
(aset w 0 'fu)
     => fu
w
     => [fu bar baz]
(setq x "asdfasfd")
     => "asdfasfd"
(aset x 3 ?Z)
     => 90
x
     => "asdZasfd"

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

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 [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 "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.