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In Emacs Lisp, a sequence is either a list or an array. The common property of all sequences is that they are ordered collections of elements. This section describes functions that accept any kind of sequence.
This function returns the number of elements in sequence. If sequence is a cons cell that is not a list (because the final cdr is not
nil
), awrong-type-argument
error is signaled.See List Elements, for the related function
safe-length
.(length '(1 2 3)) => 3 (length ()) => 0 (length "foobar") => 6 (length [1 2 3]) => 3 (length (make-bool-vector 5 nil)) => 5
This function returns the element of sequence indexed by index. Legitimate values of index are integers ranging from 0 up to one less than the length of sequence. If sequence is a list, then out-of-range values of index return
nil
; otherwise, they trigger anargs-out-of-range
error.(elt [1 2 3 4] 2) => 3 (elt '(1 2 3 4) 2) => 3 ;; We usestring
to show clearly which characterelt
returns. (string (elt "1234" 2)) => "3" (elt [1 2 3 4] 4) error--> Args out of range: [1 2 3 4], 4 (elt [1 2 3 4] -1) error--> Args out of range: [1 2 3 4], -1This function generalizes
aref
(see Array Functions) andnth
(see List Elements).
Returns a copy of sequence. The copy is the same type of object as the original sequence, and it has the same elements in the same order.
Storing a new element into the copy does not affect the original sequence, and vice versa. However, the elements of the new sequence are not copies; they are identical (
eq
) to the elements of the original. Therefore, changes made within these elements, as found via the copied sequence, are also visible in the original sequence.If the sequence is a string with text properties, the property list in the copy is itself a copy, not shared with the original's property list. However, the actual values of the properties are shared. See Text Properties.
See also
append
in Building Lists,concat
in Creating Strings, andvconcat
in Vectors, for other ways to copy sequences.(setq bar '(1 2)) => (1 2) (setq x (vector 'foo bar)) => [foo (1 2)] (setq y (copy-sequence x)) => [foo (1 2)] (eq x y) => nil (equal x y) => t (eq (elt x 1) (elt y 1)) => t ;; Replacing an element of one sequence. (aset x 0 'quux) x => [quux (1 2)] y => [foo (1 2)] ;; Modifying the inside of a shared element. (setcar (aref x 1) 69) x => [quux (69 2)] y => [foo (69 2)]