12.3 Functions that Operate on Arrays

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

Function: arrayp object

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

(arrayp "asdf")
⇒ t
(arrayp [a])
⇒ t
(arrayp #*101)
⇒ 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)
     ⇒ ?b

(aref #*1101 2)
     ⇒ 0

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)
     ⇒ ?Z
x
     ⇒ "asdZasfd"

(setq bv #*1111)
     ⇒ #*1111
(aset bv 2 0)
     ⇒ 0
bv
     ⇒ #*1101

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 ?-)
     ⇒ "------------------"

(setq bv #*1101)
     ⇒ #*1101
(fillarray bv 0)
     ⇒ #*0000

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.