2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001,
4 @c 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
5 @c Free Software Foundation, Inc.
6 @c See the file elisp.texi for copying conditions.
7 @setfilename ../../info/sequences
8 @node Sequences Arrays Vectors, Hash Tables, Lists, Top
9 @chapter Sequences, Arrays, and Vectors
12 Recall that the @dfn{sequence} type is the union of two other Lisp
13 types: lists and arrays. In other words, any list is a sequence, and
14 any array is a sequence. The common property that all sequences have is
15 that each is an ordered collection of elements.
17 An @dfn{array} is a fixed-length object with a slot for each of its
18 elements. All the elements are accessible in constant time. The four
19 types of arrays are strings, vectors, char-tables and bool-vectors.
21 A list is a sequence of elements, but it is not a single primitive
22 object; it is made of cons cells, one cell per element. Finding the
23 @var{n}th element requires looking through @var{n} cons cells, so
24 elements farther from the beginning of the list take longer to access.
25 But it is possible to add elements to the list, or remove elements.
27 The following diagram shows the relationship between these types:
31 _____________________________________________
34 | ______ ________________________________ |
36 | | List | | Array | |
37 | | | | ________ ________ | |
38 | |______| | | | | | | |
39 | | | Vector | | String | | |
40 | | |________| |________| | |
41 | | ____________ _____________ | |
43 | | | Char-table | | Bool-vector | | |
44 | | |____________| |_____________| | |
45 | |________________________________| |
46 |_____________________________________________|
51 * Sequence Functions:: Functions that accept any kind of sequence.
52 * Arrays:: Characteristics of arrays in Emacs Lisp.
53 * Array Functions:: Functions specifically for arrays.
54 * Vectors:: Special characteristics of Emacs Lisp vectors.
55 * Vector Functions:: Functions specifically for vectors.
56 * Char-Tables:: How to work with char-tables.
57 * Bool-Vectors:: How to work with bool-vectors.
60 @node Sequence Functions
63 In Emacs Lisp, a @dfn{sequence} is either a list or an array. The
64 common property of all sequences is that they are ordered collections of
65 elements. This section describes functions that accept any kind of
68 @defun sequencep object
69 Returns @code{t} if @var{object} is a list, vector, string,
70 bool-vector, or char-table, @code{nil} otherwise.
73 @defun length sequence
77 @cindex sequence length
78 @cindex char-table length
79 This function returns the number of elements in @var{sequence}. If
80 @var{sequence} is a dotted list, a @code{wrong-type-argument} error is
81 signaled. Circular lists may cause an infinite loop. For a
82 char-table, the value returned is always one more than the maximum
85 @xref{Definition of safe-length}, for the related function @code{safe-length}.
105 (length (make-bool-vector 5 nil))
112 See also @code{string-bytes}, in @ref{Text Representations}.
114 @defun elt sequence index
115 @cindex elements of sequences
116 This function returns the element of @var{sequence} indexed by
117 @var{index}. Legitimate values of @var{index} are integers ranging
118 from 0 up to one less than the length of @var{sequence}. If
119 @var{sequence} is a list, out-of-range values behave as for
120 @code{nth}. @xref{Definition of nth}. Otherwise, out-of-range values
121 trigger an @code{args-out-of-range} error.
133 ;; @r{We use @code{string} to show clearly which character @code{elt} returns.}
134 (string (elt "1234" 2))
139 @error{} Args out of range: [1 2 3 4], 4
143 @error{} Args out of range: [1 2 3 4], -1
147 This function generalizes @code{aref} (@pxref{Array Functions}) and
148 @code{nth} (@pxref{Definition of nth}).
151 @defun copy-sequence sequence
152 @cindex copying sequences
153 Returns a copy of @var{sequence}. The copy is the same type of object
154 as the original sequence, and it has the same elements in the same order.
156 Storing a new element into the copy does not affect the original
157 @var{sequence}, and vice versa. However, the elements of the new
158 sequence are not copies; they are identical (@code{eq}) to the elements
159 of the original. Therefore, changes made within these elements, as
160 found via the copied sequence, are also visible in the original
163 If the sequence is a string with text properties, the property list in
164 the copy is itself a copy, not shared with the original's property
165 list. However, the actual values of the properties are shared.
166 @xref{Text Properties}.
168 This function does not work for dotted lists. Trying to copy a
169 circular list may cause an infinite loop.
171 See also @code{append} in @ref{Building Lists}, @code{concat} in
172 @ref{Creating Strings}, and @code{vconcat} in @ref{Vector Functions},
173 for other ways to copy sequences.
181 (setq x (vector 'foo bar))
182 @result{} [foo (1 2)]
185 (setq y (copy-sequence x))
186 @result{} [foo (1 2)]
198 (eq (elt x 1) (elt y 1))
203 ;; @r{Replacing an element of one sequence.}
205 x @result{} [quux (1 2)]
206 y @result{} [foo (1 2)]
210 ;; @r{Modifying the inside of a shared element.}
211 (setcar (aref x 1) 69)
212 x @result{} [quux (69 2)]
213 y @result{} [foo (69 2)]
222 An @dfn{array} object has slots that hold a number of other Lisp
223 objects, called the elements of the array. Any element of an array
224 may be accessed in constant time. In contrast, the time to access an
225 element of a list is proportional to the position of that element in
228 Emacs defines four types of array, all one-dimensional:
229 @dfn{strings} (@pxref{String Type}), @dfn{vectors} (@pxref{Vector
230 Type}), @dfn{bool-vectors} (@pxref{Bool-Vector Type}), and
231 @dfn{char-tables} (@pxref{Char-Table Type}). Vectors and char-tables
232 can hold elements of any type, but strings can only hold characters,
233 and bool-vectors can only hold @code{t} and @code{nil}.
235 All four kinds of array share these characteristics:
239 The first element of an array has index zero, the second element has
240 index 1, and so on. This is called @dfn{zero-origin} indexing. For
241 example, an array of four elements has indices 0, 1, 2, @w{and 3}.
244 The length of the array is fixed once you create it; you cannot
245 change the length of an existing array.
248 For purposes of evaluation, the array is a constant---in other words,
249 it evaluates to itself.
252 The elements of an array may be referenced or changed with the functions
253 @code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
256 When you create an array, other than a char-table, you must specify
257 its length. You cannot specify the length of a char-table, because that
258 is determined by the range of character codes.
260 In principle, if you want an array of text characters, you could use
261 either a string or a vector. In practice, we always choose strings for
262 such applications, for four reasons:
266 They occupy one-fourth the space of a vector of the same elements.
269 Strings are printed in a way that shows the contents more clearly
273 Strings can hold text properties. @xref{Text Properties}.
276 Many of the specialized editing and I/O facilities of Emacs accept only
277 strings. For example, you cannot insert a vector of characters into a
278 buffer the way you can insert a string. @xref{Strings and Characters}.
281 By contrast, for an array of keyboard input characters (such as a key
282 sequence), a vector may be necessary, because many keyboard input
283 characters are outside the range that will fit in a string. @xref{Key
286 @node Array Functions
287 @section Functions that Operate on Arrays
289 In this section, we describe the functions that accept all types of
293 This function returns @code{t} if @var{object} is an array (i.e., a
294 vector, a string, a bool-vector or a char-table).
302 (arrayp (syntax-table)) ;; @r{A char-table.}
308 @defun aref array index
309 @cindex array elements
310 This function returns the @var{index}th element of @var{array}. The
311 first element is at index zero.
315 (setq primes [2 3 5 7 11 13])
316 @result{} [2 3 5 7 11 13]
322 @result{} 98 ; @r{@samp{b} is @acronym{ASCII} code 98.}
326 See also the function @code{elt}, in @ref{Sequence Functions}.
329 @defun aset array index object
330 This function sets the @var{index}th element of @var{array} to be
331 @var{object}. It returns @var{object}.
335 (setq w [foo bar baz])
336 @result{} [foo bar baz]
340 @result{} [fu bar baz]
353 If @var{array} is a string and @var{object} is not a character, a
354 @code{wrong-type-argument} error results. The function converts a
355 unibyte string to multibyte if necessary to insert a character.
358 @defun fillarray array object
359 This function fills the array @var{array} with @var{object}, so that
360 each element of @var{array} is @var{object}. It returns @var{array}.
364 (setq a [a b c d e f g])
365 @result{} [a b c d e f g]
367 @result{} [0 0 0 0 0 0 0]
369 @result{} [0 0 0 0 0 0 0]
372 (setq s "When in the course")
373 @result{} "When in the course"
375 @result{} "------------------"
379 If @var{array} is a string and @var{object} is not a character, a
380 @code{wrong-type-argument} error results.
383 The general sequence functions @code{copy-sequence} and @code{length}
384 are often useful for objects known to be arrays. @xref{Sequence Functions}.
388 @cindex vector (type)
390 A @dfn{vector} is a general-purpose array whose elements can be any
391 Lisp objects. (By contrast, the elements of a string can only be
392 characters. @xref{Strings and Characters}.) Vectors are used in
393 Emacs for many purposes: as key sequences (@pxref{Key Sequences}), as
394 symbol-lookup tables (@pxref{Creating Symbols}), as part of the
395 representation of a byte-compiled function (@pxref{Byte Compilation}),
398 In Emacs Lisp, the indices of the elements of a vector start from zero
399 and count up from there.
401 Vectors are printed with square brackets surrounding the elements.
402 Thus, a vector whose elements are the symbols @code{a}, @code{b} and
403 @code{a} is printed as @code{[a b a]}. You can write vectors in the
404 same way in Lisp input.
406 A vector, like a string or a number, is considered a constant for
407 evaluation: the result of evaluating it is the same vector. This does
408 not evaluate or even examine the elements of the vector.
409 @xref{Self-Evaluating Forms}.
411 Here are examples illustrating these principles:
415 (setq avector [1 two '(three) "four" [five]])
416 @result{} [1 two (quote (three)) "four" [five]]
418 @result{} [1 two (quote (three)) "four" [five]]
419 (eq avector (eval avector))
424 @node Vector Functions
425 @section Functions for Vectors
427 Here are some functions that relate to vectors:
429 @defun vectorp object
430 This function returns @code{t} if @var{object} is a vector.
442 @defun vector &rest objects
443 This function creates and returns a vector whose elements are the
444 arguments, @var{objects}.
448 (vector 'foo 23 [bar baz] "rats")
449 @result{} [foo 23 [bar baz] "rats"]
456 @defun make-vector length object
457 This function returns a new vector consisting of @var{length} elements,
458 each initialized to @var{object}.
462 (setq sleepy (make-vector 9 'Z))
463 @result{} [Z Z Z Z Z Z Z Z Z]
468 @defun vconcat &rest sequences
469 @cindex copying vectors
470 This function returns a new vector containing all the elements of
471 @var{sequences}. The arguments @var{sequences} may be true lists,
472 vectors, strings or bool-vectors. If no @var{sequences} are given, an
473 empty vector is returned.
475 The value is a newly constructed vector that is not @code{eq} to any
480 (setq a (vconcat '(A B C) '(D E F)))
481 @result{} [A B C D E F]
488 (vconcat [A B C] "aa" '(foo (6 7)))
489 @result{} [A B C 97 97 foo (6 7)]
493 The @code{vconcat} function also allows byte-code function objects as
494 arguments. This is a special feature to make it easy to access the entire
495 contents of a byte-code function object. @xref{Byte-Code Objects}.
497 For other concatenation functions, see @code{mapconcat} in @ref{Mapping
498 Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
499 in @ref{Building Lists}.
502 The @code{append} function also provides a way to convert a vector into a
503 list with the same elements:
507 (setq avector [1 two (quote (three)) "four" [five]])
508 @result{} [1 two (quote (three)) "four" [five]]
510 @result{} (1 two (quote (three)) "four" [five])
517 @cindex extra slots of char-table
519 A char-table is much like a vector, except that it is indexed by
520 character codes. Any valid character code, without modifiers, can be
521 used as an index in a char-table. You can access a char-table's
522 elements with @code{aref} and @code{aset}, as with any array. In
523 addition, a char-table can have @dfn{extra slots} to hold additional
524 data not associated with particular character codes. Like vectors,
525 char-tables are constants when evaluated, and can hold elements of any
528 @cindex subtype of char-table
529 Each char-table has a @dfn{subtype}, a symbol, which serves two
534 The subtype provides an easy way to tell what the char-table is for.
535 For instance, display tables are char-tables with @code{display-table}
536 as the subtype, and syntax tables are char-tables with
537 @code{syntax-table} as the subtype. The subtype can be queried using
538 the function @code{char-table-subtype}, described below.
541 The subtype controls the number of @dfn{extra slots} in the
542 char-table. This number is specified by the subtype's
543 @code{char-table-extra-slots} symbol property, which should be an
544 integer between 0 and 10. If the subtype has no such symbol property,
545 the char-table has no extra slots. @xref{Property Lists}, for
546 information about symbol properties.
549 @cindex parent of char-table
550 A char-table can have a @dfn{parent}, which is another char-table. If
551 it does, then whenever the char-table specifies @code{nil} for a
552 particular character @var{c}, it inherits the value specified in the
553 parent. In other words, @code{(aref @var{char-table} @var{c})} returns
554 the value from the parent of @var{char-table} if @var{char-table} itself
555 specifies @code{nil}.
557 @cindex default value of char-table
558 A char-table can also have a @dfn{default value}. If so, then
559 @code{(aref @var{char-table} @var{c})} returns the default value
560 whenever the char-table does not specify any other non-@code{nil} value.
562 @defun make-char-table subtype &optional init
563 Return a newly-created char-table, with subtype @var{subtype} (a
564 symbol). Each element is initialized to @var{init}, which defaults to
565 @code{nil}. You cannot alter the subtype of a char-table after the
566 char-table is created.
568 There is no argument to specify the length of the char-table, because
569 all char-tables have room for any valid character code as an index.
571 If @var{subtype} has the @code{char-table-extra-slots} symbol
572 property, that specifies the number of extra slots in the char-table.
573 This should be an integer between 0 and 10; otherwise,
574 @code{make-char-table} raises an error. If @var{subtype} has no
575 @code{char-table-extra-slots} symbol property (@pxref{Property
576 Lists}), the char-table has no extra slots.
579 @defun char-table-p object
580 This function returns @code{t} if @var{object} is a char-table, and
581 @code{nil} otherwise.
584 @defun char-table-subtype char-table
585 This function returns the subtype symbol of @var{char-table}.
588 There is no special function to access default values in a char-table.
589 To do that, use @code{char-table-range} (see below).
591 @defun char-table-parent char-table
592 This function returns the parent of @var{char-table}. The parent is
593 always either @code{nil} or another char-table.
596 @defun set-char-table-parent char-table new-parent
597 This function sets the parent of @var{char-table} to @var{new-parent}.
600 @defun char-table-extra-slot char-table n
601 This function returns the contents of extra slot @var{n} of
602 @var{char-table}. The number of extra slots in a char-table is
603 determined by its subtype.
606 @defun set-char-table-extra-slot char-table n value
607 This function stores @var{value} in extra slot @var{n} of
611 A char-table can specify an element value for a single character code;
612 it can also specify a value for an entire character set.
614 @defun char-table-range char-table range
615 This returns the value specified in @var{char-table} for a range of
616 characters @var{range}. Here are the possibilities for @var{range}:
620 Refers to the default value.
623 Refers to the element for character @var{char}
624 (supposing @var{char} is a valid character code).
626 @item @code{(@var{from} . @var{to})}
627 A cons cell refers to all the characters in the inclusive range
628 @samp{[@var{from}..@var{to}]}.
632 @defun set-char-table-range char-table range value
633 This function sets the value in @var{char-table} for a range of
634 characters @var{range}. Here are the possibilities for @var{range}:
638 Refers to the default value.
641 Refers to the whole range of character codes.
644 Refers to the element for character @var{char}
645 (supposing @var{char} is a valid character code).
647 @item @code{(@var{from} . @var{to})}
648 A cons cell refers to all the characters in the inclusive range
649 @samp{[@var{from}..@var{to}]}.
653 @defun map-char-table function char-table
654 This function calls its argument @var{function} for each element of
655 @var{char-table} that has a non-@code{nil} value. The call to
656 @var{function} is with two arguments, a key and a value. The key
657 is a possible @var{range} argument for @code{char-table-range}---either
658 a valid character or a cons cell @code{(@var{from} . @var{to})},
659 specifying a range of characters that share the same value. The value is
660 what @code{(char-table-range @var{char-table} @var{key})} returns.
662 Overall, the key-value pairs passed to @var{function} describe all the
663 values stored in @var{char-table}.
665 The return value is always @code{nil}; to make calls to
666 @code{map-char-table} useful, @var{function} should have side effects.
667 For example, here is how to examine the elements of the syntax table:
672 #'(lambda (key value)
676 (list (car key) (cdr key))
683 (((2597602 4194303) (2)) ((2597523 2597601) (3))
684 ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))
685 ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
690 @section Bool-vectors
693 A bool-vector is much like a vector, except that it stores only the
694 values @code{t} and @code{nil}. If you try to store any non-@code{nil}
695 value into an element of the bool-vector, the effect is to store
696 @code{t} there. As with all arrays, bool-vector indices start from 0,
697 and the length cannot be changed once the bool-vector is created.
698 Bool-vectors are constants when evaluated.
700 There are two special functions for working with bool-vectors; aside
701 from that, you manipulate them with same functions used for other kinds
704 @defun make-bool-vector length initial
705 Return a new bool-vector of @var{length} elements,
706 each one initialized to @var{initial}.
709 @defun bool-vector-p object
710 This returns @code{t} if @var{object} is a bool-vector,
711 and @code{nil} otherwise.
714 Here is an example of creating, examining, and updating a
715 bool-vector. Note that the printed form represents up to 8 boolean
716 values as a single character.
719 (setq bv (make-bool-vector 5 t))
730 These results make sense because the binary codes for control-_ and
731 control-W are 11111 and 10111, respectively.
734 arch-tag: fcf1084a-cd29-4adc-9f16-68586935b386