2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2016 Free Software
5 @c See the file elisp.texi for copying conditions.
6 @node Sequences Arrays Vectors
7 @chapter Sequences, Arrays, and Vectors
10 The @dfn{sequence} type is the union of two other Lisp types: lists
11 and arrays. In other words, any list is a sequence, and any array is
12 a sequence. The common property that all sequences have is that each
13 is an ordered collection of elements.
15 An @dfn{array} is a fixed-length object with a slot for each of its
16 elements. All the elements are accessible in constant time. The four
17 types of arrays are strings, vectors, char-tables and bool-vectors.
19 A list is a sequence of elements, but it is not a single primitive
20 object; it is made of cons cells, one cell per element. Finding the
21 @var{n}th element requires looking through @var{n} cons cells, so
22 elements farther from the beginning of the list take longer to access.
23 But it is possible to add elements to the list, or remove elements.
25 The following diagram shows the relationship between these types:
29 _____________________________________________
32 | ______ ________________________________ |
34 | | List | | Array | |
35 | | | | ________ ________ | |
36 | |______| | | | | | | |
37 | | | Vector | | String | | |
38 | | |________| |________| | |
39 | | ____________ _____________ | |
41 | | | Char-table | | Bool-vector | | |
42 | | |____________| |_____________| | |
43 | |________________________________| |
44 |_____________________________________________|
49 * Sequence Functions:: Functions that accept any kind of sequence.
50 * Arrays:: Characteristics of arrays in Emacs Lisp.
51 * Array Functions:: Functions specifically for arrays.
52 * Vectors:: Special characteristics of Emacs Lisp vectors.
53 * Vector Functions:: Functions specifically for vectors.
54 * Char-Tables:: How to work with char-tables.
55 * Bool-Vectors:: How to work with bool-vectors.
56 * Rings:: Managing a fixed-size ring of objects.
59 @node Sequence Functions
62 This section describes functions that accept any kind of sequence.
64 @defun sequencep object
65 This function returns @code{t} if @var{object} is a list, vector,
66 string, bool-vector, or char-table, @code{nil} otherwise.
69 @defun length sequence
73 @cindex sequence length
74 @cindex char-table length
75 @anchor{Definition of length}
76 This function returns the number of elements in @var{sequence}. If
77 @var{sequence} is a dotted list, a @code{wrong-type-argument} error is
78 signaled. Circular lists may cause an infinite loop. For a
79 char-table, the value returned is always one more than the maximum
82 @xref{Definition of safe-length}, for the related function @code{safe-length}.
102 (length (make-bool-vector 5 nil))
109 See also @code{string-bytes}, in @ref{Text Representations}.
111 If you need to compute the width of a string on display, you should use
112 @code{string-width} (@pxref{Size of Displayed Text}), not @code{length},
113 since @code{length} only counts the number of characters, but does not
114 account for the display width of each character.
116 @defun elt sequence index
117 @anchor{Definition of elt}
118 @cindex elements of sequences
119 This function returns the element of @var{sequence} indexed by
120 @var{index}. Legitimate values of @var{index} are integers ranging
121 from 0 up to one less than the length of @var{sequence}. If
122 @var{sequence} is a list, out-of-range values behave as for
123 @code{nth}. @xref{Definition of nth}. Otherwise, out-of-range values
124 trigger an @code{args-out-of-range} error.
136 ;; @r{We use @code{string} to show clearly which character @code{elt} returns.}
137 (string (elt "1234" 2))
142 @error{} Args out of range: [1 2 3 4], 4
146 @error{} Args out of range: [1 2 3 4], -1
150 This function generalizes @code{aref} (@pxref{Array Functions}) and
151 @code{nth} (@pxref{Definition of nth}).
154 @defun copy-sequence sequence
155 @cindex copying sequences
156 This function returns a copy of @var{sequence}. The copy is the same
157 type of object as the original sequence, and it has the same elements
160 Storing a new element into the copy does not affect the original
161 @var{sequence}, and vice versa. However, the elements of the new
162 sequence are not copies; they are identical (@code{eq}) to the elements
163 of the original. Therefore, changes made within these elements, as
164 found via the copied sequence, are also visible in the original
167 If the sequence is a string with text properties, the property list in
168 the copy is itself a copy, not shared with the original's property
169 list. However, the actual values of the properties are shared.
170 @xref{Text Properties}.
172 This function does not work for dotted lists. Trying to copy a
173 circular list may cause an infinite loop.
175 See also @code{append} in @ref{Building Lists}, @code{concat} in
176 @ref{Creating Strings}, and @code{vconcat} in @ref{Vector Functions},
177 for other ways to copy sequences.
185 (setq x (vector 'foo bar))
186 @result{} [foo (1 2)]
189 (setq y (copy-sequence x))
190 @result{} [foo (1 2)]
202 (eq (elt x 1) (elt y 1))
207 ;; @r{Replacing an element of one sequence.}
209 x @result{} [quux (1 2)]
210 y @result{} [foo (1 2)]
214 ;; @r{Modifying the inside of a shared element.}
215 (setcar (aref x 1) 69)
216 x @result{} [quux (69 2)]
217 y @result{} [foo (69 2)]
222 @defun reverse sequence
223 @cindex string reverse
225 @cindex vector reverse
226 @cindex sequence reverse
227 This function creates a new sequence whose elements are the elements
228 of @var{sequence}, but in reverse order. The original argument @var{sequence}
229 is @emph{not} altered. Note that char-tables cannot be reversed.
265 @defun nreverse sequence
266 @cindex reversing a string
267 @cindex reversing a list
268 @cindex reversing a vector
269 This function reverses the order of the elements of @var{sequence}.
270 Unlike @code{reverse} the original @var{sequence} may be modified.
286 ;; @r{The cons cell that was first is now last.}
292 To avoid confusion, we usually store the result of @code{nreverse}
293 back in the same variable which held the original list:
296 (setq x (nreverse x))
299 Here is the @code{nreverse} of our favorite example, @code{(a b c)},
300 presented graphically:
304 @r{Original list head:} @r{Reversed list:}
305 ------------- ------------- ------------
306 | car | cdr | | car | cdr | | car | cdr |
307 | a | nil |<-- | b | o |<-- | c | o |
308 | | | | | | | | | | | | |
309 ------------- | --------- | - | -------- | -
311 ------------- ------------
315 For the vector, it is even simpler because you don't need setq:
326 Note that unlike @code{reverse}, this function doesn't work with strings.
327 Although you can alter string data by using @code{aset}, it is strongly
328 encouraged to treat strings as immutable.
332 @defun sort sequence predicate
334 @cindex sorting lists
335 @cindex sorting vectors
336 This function sorts @var{sequence} stably. Note that this function doesn't work
337 for all sequences; it may be used only for lists and vectors. If @var{sequence}
338 is a list, it is modified destructively. This functions returns the sorted
339 @var{sequence} and compares elements using @var{predicate}. A stable sort is
340 one in which elements with equal sort keys maintain their relative order before
341 and after the sort. Stability is important when successive sorts are used to
342 order elements according to different criteria.
344 The argument @var{predicate} must be a function that accepts two
345 arguments. It is called with two elements of @var{sequence}. To get an
346 increasing order sort, the @var{predicate} should return non-@code{nil} if the
347 first element is ``less'' than the second, or @code{nil} if not.
349 The comparison function @var{predicate} must give reliable results for
350 any given pair of arguments, at least within a single call to
351 @code{sort}. It must be @dfn{antisymmetric}; that is, if @var{a} is
352 less than @var{b}, @var{b} must not be less than @var{a}. It must be
353 @dfn{transitive}---that is, if @var{a} is less than @var{b}, and @var{b}
354 is less than @var{c}, then @var{a} must be less than @var{c}. If you
355 use a comparison function which does not meet these requirements, the
356 result of @code{sort} is unpredictable.
358 The destructive aspect of @code{sort} for lists is that it rearranges the
359 cons cells forming @var{sequence} by changing @sc{cdr}s. A nondestructive
360 sort function would create new cons cells to store the elements in their
361 sorted order. If you wish to make a sorted copy without destroying the
362 original, copy it first with @code{copy-sequence} and then sort.
364 Sorting does not change the @sc{car}s of the cons cells in @var{sequence};
365 the cons cell that originally contained the element @code{a} in
366 @var{sequence} still has @code{a} in its @sc{car} after sorting, but it now
367 appears in a different position in the list due to the change of
368 @sc{cdr}s. For example:
372 (setq nums '(1 3 2 6 5 4 0))
373 @result{} (1 3 2 6 5 4 0)
377 @result{} (0 1 2 3 4 5 6)
381 @result{} (1 2 3 4 5 6)
386 @strong{Warning}: Note that the list in @code{nums} no longer contains
387 0; this is the same cons cell that it was before, but it is no longer
388 the first one in the list. Don't assume a variable that formerly held
389 the argument now holds the entire sorted list! Instead, save the result
390 of @code{sort} and use that. Most often we store the result back into
391 the variable that held the original list:
394 (setq nums (sort nums '<))
397 For the better understanding of what stable sort is, consider the following
398 vector example. After sorting, all items whose @code{car} is 8 are grouped
399 at the beginning of @code{vector}, but their relative order is preserved.
400 All items whose @code{car} is 9 are grouped at the end of @code{vector},
401 but their relative order is also preserved:
407 (vector '(8 . "xxx") '(9 . "aaa") '(8 . "bbb") '(9 . "zzz")
408 '(9 . "ppp") '(8 . "ttt") '(8 . "eee") '(9 . "fff")))
409 @result{} [(8 . "xxx") (9 . "aaa") (8 . "bbb") (9 . "zzz")
410 (9 . "ppp") (8 . "ttt") (8 . "eee") (9 . "fff")]
413 (sort vector (lambda (x y) (< (car x) (car y))))
414 @result{} [(8 . "xxx") (8 . "bbb") (8 . "ttt") (8 . "eee")
415 (9 . "aaa") (9 . "zzz") (9 . "ppp") (9 . "fff")]
419 @xref{Sorting}, for more functions that perform sorting.
420 See @code{documentation} in @ref{Accessing Documentation}, for a
421 useful example of @code{sort}.
424 @cindex sequence functions in seq
426 The @file{seq.el} library provides the following additional sequence
427 manipulation macros and functions, prefixed with @code{seq-}. To use
428 them, you must first load the @file{seq} library.
430 All functions defined in this library are free of side-effects;
431 i.e., they do not modify any sequence (list, vector, or string) that
432 you pass as an argument. Unless otherwise stated, the result is a
433 sequence of the same type as the input. For those functions that take
434 a predicate, this should be a function of one argument.
436 The @file{seq.el} library can be extended to work with additional
437 types of sequential data-structures. For that purpose, all functions
438 are defined using @code{cl-defgeneric}. @xref{Generic Functions}, for
439 more details about using @code{cl-defgeneric} for adding extensions.
441 @defun seq-elt sequence index
442 This function returns the element of @var{sequence} at the specified
443 @var{index}, which is an integer whose valid value range is zero to
444 one less than the length of @var{sequence}. For out-of-range values
445 on built-in sequence types, @code{seq-elt} behaves like @code{elt}.
446 For the details, see @ref{Definition of elt}.
450 (seq-elt [1 2 3 4] 2)
455 @code{seq-elt} returns places settable using @code{setf}
456 (@pxref{Setting Generalized Variables}).
461 (setf (seq-elt vec 2) 5)
468 @defun seq-length sequence
469 This function returns the number of elements in @var{sequence}. For
470 built-in sequence types, @code{seq-length} behaves like @code{length}.
471 @xref{Definition of length}.
475 This function returns non-@code{nil} if @var{sequence} is a sequence
476 (a list or array), or any additional type of sequence defined via
477 @file{seq.el} generic functions.
491 @defun seq-drop sequence n
492 This function returns all but the first @var{n} (an integer)
493 elements of @var{sequence}. If @var{n} is negative or zero,
494 the result is @var{sequence}.
498 (seq-drop [1 2 3 4 5 6] 3)
502 (seq-drop "hello world" -4)
503 @result{} "hello world"
508 @defun seq-take sequence n
509 This function returns the first @var{n} (an integer) elements of
510 @var{sequence}. If @var{n} is negative or zero, the result
515 (seq-take '(1 2 3 4) 3)
519 (seq-take [1 2 3 4] 0)
525 @defun seq-take-while predicate sequence
526 This function returns the members of @var{sequence} in order,
527 stopping before the first one for which @var{predicate} returns @code{nil}.
531 (seq-take-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
535 (seq-take-while (lambda (elt) (> elt 0)) [-1 4 6])
541 @defun seq-drop-while predicate sequence
542 This function returns the members of @var{sequence} in order,
543 starting from the first one for which @var{predicate} returns @code{nil}.
547 (seq-drop-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
551 (seq-drop-while (lambda (elt) (< elt 0)) [1 4 6])
557 @defun seq-do function sequence
558 This function applies @var{function} to each element of
559 @var{sequence} in turn (presumably for side effects), and returns
563 @defun seq-map function sequence
564 This function returns the result of applying @var{function} to each
565 element of @var{sequence}. The returned value is a list.
569 (seq-map #'1+ '(2 4 6))
573 (seq-map #'symbol-name [foo bar])
574 @result{} ("foo" "bar")
579 @defun seq-mapn function &rest sequences
580 This function returns the result of applying @var{function} to each
581 element of @var{sequences}. The arity (@pxref{What Is a Function,
582 sub-arity}) of @var{function} must match the number of sequences.
583 Mapping stops at the end of the shortest sequence, and the returned
588 (seq-mapn #'+ '(2 4 6) '(20 40 60))
592 (seq-mapn #'concat '("moskito" "bite") ["bee" "sting"])
593 @result{} ("moskitobee" "bitesting")
598 @defun seq-filter predicate sequence
599 @cindex filtering sequences
600 This function returns a list of all the elements in @var{sequence}
601 for which @var{predicate} returns non-@code{nil}.
605 (seq-filter (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
609 (seq-filter (lambda (elt) (> elt 0)) '(-1 -3 -5))
615 @defun seq-remove predicate sequence
616 @cindex removing from sequences
617 This function returns a list of all the elements in @var{sequence}
618 for which @var{predicate} returns @code{nil}.
622 (seq-remove (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
626 (seq-remove (lambda (elt) (< elt 0)) '(-1 -3 -5))
632 @defun seq-reduce function sequence initial-value
633 @cindex reducing sequences
634 This function returns the result of calling @var{function} with
635 @var{initial-value} and the first element of @var{sequence}, then calling
636 @var{function} with that result and the second element of @var{sequence},
637 then with that result and the third element of @var{sequence}, etc.
638 @var{function} should be a function of two arguments. If
639 @var{sequence} is empty, this returns @var{initial-value} without
640 calling @var{function}.
644 (seq-reduce #'+ [1 2 3 4] 0)
648 (seq-reduce #'+ '(1 2 3 4) 5)
652 (seq-reduce #'+ '() 3)
658 @defun seq-some predicate sequence
659 This function returns the first non-@code{nil} value returned by
660 applying @var{predicate} to each element of @var{sequence} in turn.
664 (seq-some #'numberp ["abc" 1 nil])
668 (seq-some #'numberp ["abc" "def"])
672 (seq-some #'null ["abc" 1 nil])
676 (seq-some #'1+ [2 4 6])
682 @defun seq-find predicate sequence &optional default
683 This function returns the first element in @var{sequence} for which
684 @var{predicate} returns non-@code{nil}. If no element matches
685 @var{predicate}, the function returns @var{default}.
687 Note that this function has an ambiguity if the found element is
688 identical to @var{default}, as in that case it cannot be known whether
689 an element was found or not.
693 (seq-find #'numberp ["abc" 1 nil])
697 (seq-find #'numberp ["abc" "def"])
703 @defun seq-every-p predicate sequence
704 This function returns non-@code{nil} if applying @var{predicate}
705 to every element of @var{sequence} returns non-@code{nil}.
709 (seq-every-p #'numberp [2 4 6])
713 (seq-some #'numberp [2 4 "6"])
719 @defun seq-empty-p sequence
720 This function returns non-@code{nil} if @var{sequence} is empty.
724 (seq-empty-p "not empty")
734 @defun seq-count predicate sequence
735 This function returns the number of elements in @var{sequence} for which
736 @var{predicate} returns non-@code{nil}.
739 (seq-count (lambda (elt) (> elt 0)) [-1 2 0 3 -2])
744 @cindex sorting sequences
745 @defun seq-sort function sequence
746 This function returns a copy of @var{sequence} that is sorted
747 according to @var{function}, a function of two arguments that returns
748 non-@code{nil} if the first argument should sort before the second.
751 @defun seq-contains sequence elt &optional function
752 This function returns the first element in @var{sequence} that is equal to
753 @var{elt}. If the optional argument @var{function} is non-@code{nil},
754 it is a function of two arguments to use instead of the default @code{equal}.
758 (seq-contains '(symbol1 symbol2) 'symbol1)
762 (seq-contains '(symbol1 symbol2) 'symbol3)
769 @defun seq-position sequence elt &optional function
770 This function returns the index of the first element in
771 @var{sequence} that is equal to @var{elt}. If the optional argument
772 @var{function} is non-@code{nil}, it is a function of two arguments to
773 use instead of the default @code{equal}.
777 (seq-position '(a b c) 'b)
781 (seq-position '(a b c) 'd)
788 @defun seq-uniq sequence &optional function
789 This function returns a list of the elements of @var{sequence} with
790 duplicates removed. If the optional argument @var{function} is non-@code{nil},
791 it is a function of two arguments to use instead of the default @code{equal}.
795 (seq-uniq '(1 2 2 1 3))
799 (seq-uniq '(1 2 2.0 1.0) #'=)
805 @defun seq-subseq sequence start &optional end
806 This function returns a subset of @var{sequence} from @var{start}
807 to @var{end}, both integers (@var{end} defaults to the last element).
808 If @var{start} or @var{end} is negative, it counts from the end of
813 (seq-subseq '(1 2 3 4 5) 1)
817 (seq-subseq '[1 2 3 4 5] 1 3)
821 (seq-subseq '[1 2 3 4 5] -3 -1)
827 @defun seq-concatenate type &rest sequences
828 This function returns a sequence of type @var{type} made of the
829 concatenation of @var{sequences}. @var{type} may be: @code{vector},
830 @code{list} or @code{string}.
834 (seq-concatenate 'list '(1 2) '(3 4) [5 6])
835 @result{} (1 2 3 5 6)
838 (seq-concatenate 'string "Hello " "world")
839 @result{} "Hello world"
844 @defun seq-mapcat function sequence &optional type
845 This function returns the result of applying @code{seq-concatenate}
846 to the result of applying @var{function} to each element of
847 @var{sequence}. The result is a sequence of type @var{type}, or a
848 list if @var{type} is @code{nil}.
852 (seq-mapcat #'seq-reverse '((3 2 1) (6 5 4)))
853 @result{} (1 2 3 4 5 6)
858 @defun seq-partition sequence n
859 This function returns a list of the elements of @var{sequence}
860 grouped into sub-sequences of length @var{n}. The last sequence may
861 contain less elements than @var{n}. @var{n} must be an integer. If
862 @var{n} is a negative integer or 0, the return value is @code{nil}.
866 (seq-partition '(0 1 2 3 4 5 6 7) 3)
867 @result{} ((0 1 2) (3 4 5) (6 7))
872 @defun seq-intersection sequence1 sequence2 &optional function
873 This function returns a list of the elements that appear both in
874 @var{sequence1} and @var{sequence2}. If the optional argument
875 @var{function} is non-@code{nil}, it is a function of two arguments to
876 use to compare elements instead of the default @code{equal}.
880 (seq-intersection [2 3 4 5] [1 3 5 6 7])
887 @defun seq-difference sequence1 sequence2 &optional function
888 This function returns a list of the elements that appear in
889 @var{sequence1} but not in @var{sequence2}. If the optional argument
890 @var{function} is non-@code{nil}, it is a function of two arguments to
891 use to compare elements instead of the default @code{equal}.
895 (seq-difference '(2 3 4 5) [1 3 5 6 7])
901 @defun seq-group-by function sequence
902 This function separates the elements of @var{sequence} into an alist
903 whose keys are the result of applying @var{function} to each element
904 of @var{sequence}. Keys are compared using @code{equal}.
908 (seq-group-by #'integerp '(1 2.1 3 2 3.2))
909 @result{} ((t 1 3 2) (nil 2.1 3.2))
912 (seq-group-by #'car '((a 1) (b 2) (a 3) (c 4)))
913 @result{} ((b (b 2)) (a (a 1) (a 3)) (c (c 4)))
918 @defun seq-into sequence type
919 This function converts the sequence @var{sequence} into a sequence
920 of type @var{type}. @var{type} can be one of the following symbols:
921 @code{vector}, @code{string} or @code{list}.
925 (seq-into [1 2 3] 'list)
929 (seq-into nil 'vector)
933 (seq-into "hello" 'vector)
934 @result{} [104 101 108 108 111]
939 @defun seq-min sequence
940 This function returns the smallest element of @var{sequence}. The
941 elements of @var{sequence} must be numbers or markers
956 @defun seq-max sequence
957 This function returns the largest element of @var{sequence}. The
958 elements of @var{sequence} must be numbers or markers.
972 @defmac seq-doseq (var sequence) body@dots{}
973 @cindex sequence iteration
974 This macro is like @code{dolist} (@pxref{Iteration, dolist}), except
975 that @var{sequence} can be a list, vector or string. This is
976 primarily useful for side-effects.
979 @defmac seq-let arguments sequence body@dots{}
980 @cindex sequence destructuring
981 This macro binds the variables defined in @var{arguments} to the
982 elements of @var{sequence}. @var{arguments} can themselves include
983 sequences, allowing for nested destructuring.
985 The @var{arguments} sequence can also include the @code{&rest} marker
986 followed by a variable name to be bound to the rest of
991 (seq-let [first second] [1 2 3 4]
996 (seq-let (_ a _ b) '(1 2 3 4)
1001 (seq-let [a [b [c]]] [1 [2 [3]]]
1006 (seq-let [a b &rest others] [1 2 3 4]
1018 An @dfn{array} object has slots that hold a number of other Lisp
1019 objects, called the elements of the array. Any element of an array
1020 may be accessed in constant time. In contrast, the time to access an
1021 element of a list is proportional to the position of that element in
1024 Emacs defines four types of array, all one-dimensional:
1025 @dfn{strings} (@pxref{String Type}), @dfn{vectors} (@pxref{Vector
1026 Type}), @dfn{bool-vectors} (@pxref{Bool-Vector Type}), and
1027 @dfn{char-tables} (@pxref{Char-Table Type}). Vectors and char-tables
1028 can hold elements of any type, but strings can only hold characters,
1029 and bool-vectors can only hold @code{t} and @code{nil}.
1031 All four kinds of array share these characteristics:
1035 The first element of an array has index zero, the second element has
1036 index 1, and so on. This is called @dfn{zero-origin} indexing. For
1037 example, an array of four elements has indices 0, 1, 2, @w{and 3}.
1040 The length of the array is fixed once you create it; you cannot
1041 change the length of an existing array.
1044 For purposes of evaluation, the array is a constant---i.e.,
1045 it evaluates to itself.
1048 The elements of an array may be referenced or changed with the functions
1049 @code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
1052 When you create an array, other than a char-table, you must specify
1053 its length. You cannot specify the length of a char-table, because that
1054 is determined by the range of character codes.
1056 In principle, if you want an array of text characters, you could use
1057 either a string or a vector. In practice, we always choose strings for
1058 such applications, for four reasons:
1062 They occupy one-fourth the space of a vector of the same elements.
1065 Strings are printed in a way that shows the contents more clearly
1069 Strings can hold text properties. @xref{Text Properties}.
1072 Many of the specialized editing and I/O facilities of Emacs accept only
1073 strings. For example, you cannot insert a vector of characters into a
1074 buffer the way you can insert a string. @xref{Strings and Characters}.
1077 By contrast, for an array of keyboard input characters (such as a key
1078 sequence), a vector may be necessary, because many keyboard input
1079 characters are outside the range that will fit in a string. @xref{Key
1082 @node Array Functions
1083 @section Functions that Operate on Arrays
1085 In this section, we describe the functions that accept all types of
1088 @defun arrayp object
1089 This function returns @code{t} if @var{object} is an array (i.e., a
1090 vector, a string, a bool-vector or a char-table).
1098 (arrayp (syntax-table)) ;; @r{A char-table.}
1104 @defun aref array index
1105 @cindex array elements
1106 This function returns the @var{index}th element of @var{array}. The
1107 first element is at index zero.
1111 (setq primes [2 3 5 7 11 13])
1112 @result{} [2 3 5 7 11 13]
1118 @result{} 98 ; @r{@samp{b} is @acronym{ASCII} code 98.}
1122 See also the function @code{elt}, in @ref{Sequence Functions}.
1125 @defun aset array index object
1126 This function sets the @var{index}th element of @var{array} to be
1127 @var{object}. It returns @var{object}.
1131 (setq w [foo bar baz])
1132 @result{} [foo bar baz]
1136 @result{} [fu bar baz]
1141 @result{} "asdfasfd"
1145 @result{} "asdZasfd"
1149 If @var{array} is a string and @var{object} is not a character, a
1150 @code{wrong-type-argument} error results. The function converts a
1151 unibyte string to multibyte if necessary to insert a character.
1154 @defun fillarray array object
1155 This function fills the array @var{array} with @var{object}, so that
1156 each element of @var{array} is @var{object}. It returns @var{array}.
1160 (setq a [a b c d e f g])
1161 @result{} [a b c d e f g]
1163 @result{} [0 0 0 0 0 0 0]
1165 @result{} [0 0 0 0 0 0 0]
1168 (setq s "When in the course")
1169 @result{} "When in the course"
1171 @result{} "------------------"
1175 If @var{array} is a string and @var{object} is not a character, a
1176 @code{wrong-type-argument} error results.
1179 The general sequence functions @code{copy-sequence} and @code{length}
1180 are often useful for objects known to be arrays. @xref{Sequence Functions}.
1184 @cindex vector (type)
1186 A @dfn{vector} is a general-purpose array whose elements can be any
1187 Lisp objects. (By contrast, the elements of a string can only be
1188 characters. @xref{Strings and Characters}.) Vectors are used in
1189 Emacs for many purposes: as key sequences (@pxref{Key Sequences}), as
1190 symbol-lookup tables (@pxref{Creating Symbols}), as part of the
1191 representation of a byte-compiled function (@pxref{Byte Compilation}),
1194 Like other arrays, vectors use zero-origin indexing: the first
1195 element has index 0.
1197 Vectors are printed with square brackets surrounding the elements.
1198 Thus, a vector whose elements are the symbols @code{a}, @code{b} and
1199 @code{a} is printed as @code{[a b a]}. You can write vectors in the
1200 same way in Lisp input.
1202 A vector, like a string or a number, is considered a constant for
1203 evaluation: the result of evaluating it is the same vector. This does
1204 not evaluate or even examine the elements of the vector.
1205 @xref{Self-Evaluating Forms}.
1207 Here are examples illustrating these principles:
1211 (setq avector [1 two '(three) "four" [five]])
1212 @result{} [1 two (quote (three)) "four" [five]]
1214 @result{} [1 two (quote (three)) "four" [five]]
1215 (eq avector (eval avector))
1220 @node Vector Functions
1221 @section Functions for Vectors
1223 Here are some functions that relate to vectors:
1225 @defun vectorp object
1226 This function returns @code{t} if @var{object} is a vector.
1238 @defun vector &rest objects
1239 This function creates and returns a vector whose elements are the
1240 arguments, @var{objects}.
1244 (vector 'foo 23 [bar baz] "rats")
1245 @result{} [foo 23 [bar baz] "rats"]
1252 @defun make-vector length object
1253 This function returns a new vector consisting of @var{length} elements,
1254 each initialized to @var{object}.
1258 (setq sleepy (make-vector 9 'Z))
1259 @result{} [Z Z Z Z Z Z Z Z Z]
1264 @defun vconcat &rest sequences
1265 @cindex copying vectors
1266 This function returns a new vector containing all the elements of
1267 @var{sequences}. The arguments @var{sequences} may be true lists,
1268 vectors, strings or bool-vectors. If no @var{sequences} are given,
1269 the empty vector is returned.
1271 The value is either the empty vector, or is a newly constructed
1272 nonempty vector that is not @code{eq} to any existing vector.
1276 (setq a (vconcat '(A B C) '(D E F)))
1277 @result{} [A B C D E F]
1284 (vconcat [A B C] "aa" '(foo (6 7)))
1285 @result{} [A B C 97 97 foo (6 7)]
1289 The @code{vconcat} function also allows byte-code function objects as
1290 arguments. This is a special feature to make it easy to access the entire
1291 contents of a byte-code function object. @xref{Byte-Code Objects}.
1293 For other concatenation functions, see @code{mapconcat} in @ref{Mapping
1294 Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
1295 in @ref{Building Lists}.
1298 The @code{append} function also provides a way to convert a vector into a
1299 list with the same elements:
1303 (setq avector [1 two (quote (three)) "four" [five]])
1304 @result{} [1 two (quote (three)) "four" [five]]
1305 (append avector nil)
1306 @result{} (1 two (quote (three)) "four" [five])
1311 @section Char-Tables
1313 @cindex extra slots of char-table
1315 A char-table is much like a vector, except that it is indexed by
1316 character codes. Any valid character code, without modifiers, can be
1317 used as an index in a char-table. You can access a char-table's
1318 elements with @code{aref} and @code{aset}, as with any array. In
1319 addition, a char-table can have @dfn{extra slots} to hold additional
1320 data not associated with particular character codes. Like vectors,
1321 char-tables are constants when evaluated, and can hold elements of any
1324 @cindex subtype of char-table
1325 Each char-table has a @dfn{subtype}, a symbol, which serves two
1330 The subtype provides an easy way to tell what the char-table is for.
1331 For instance, display tables are char-tables with @code{display-table}
1332 as the subtype, and syntax tables are char-tables with
1333 @code{syntax-table} as the subtype. The subtype can be queried using
1334 the function @code{char-table-subtype}, described below.
1337 The subtype controls the number of @dfn{extra slots} in the
1338 char-table. This number is specified by the subtype's
1339 @code{char-table-extra-slots} symbol property (@pxref{Symbol
1340 Properties}), whose value should be an integer between 0 and 10. If
1341 the subtype has no such symbol property, the char-table has no extra
1345 @cindex parent of char-table
1346 A char-table can have a @dfn{parent}, which is another char-table. If
1347 it does, then whenever the char-table specifies @code{nil} for a
1348 particular character @var{c}, it inherits the value specified in the
1349 parent. In other words, @code{(aref @var{char-table} @var{c})} returns
1350 the value from the parent of @var{char-table} if @var{char-table} itself
1351 specifies @code{nil}.
1353 @cindex default value of char-table
1354 A char-table can also have a @dfn{default value}. If so, then
1355 @code{(aref @var{char-table} @var{c})} returns the default value
1356 whenever the char-table does not specify any other non-@code{nil} value.
1358 @defun make-char-table subtype &optional init
1359 Return a newly-created char-table, with subtype @var{subtype} (a
1360 symbol). Each element is initialized to @var{init}, which defaults to
1361 @code{nil}. You cannot alter the subtype of a char-table after the
1362 char-table is created.
1364 There is no argument to specify the length of the char-table, because
1365 all char-tables have room for any valid character code as an index.
1367 If @var{subtype} has the @code{char-table-extra-slots} symbol
1368 property, that specifies the number of extra slots in the char-table.
1369 This should be an integer between 0 and 10; otherwise,
1370 @code{make-char-table} raises an error. If @var{subtype} has no
1371 @code{char-table-extra-slots} symbol property (@pxref{Property
1372 Lists}), the char-table has no extra slots.
1375 @defun char-table-p object
1376 This function returns @code{t} if @var{object} is a char-table, and
1377 @code{nil} otherwise.
1380 @defun char-table-subtype char-table
1381 This function returns the subtype symbol of @var{char-table}.
1384 There is no special function to access default values in a char-table.
1385 To do that, use @code{char-table-range} (see below).
1387 @defun char-table-parent char-table
1388 This function returns the parent of @var{char-table}. The parent is
1389 always either @code{nil} or another char-table.
1392 @defun set-char-table-parent char-table new-parent
1393 This function sets the parent of @var{char-table} to @var{new-parent}.
1396 @defun char-table-extra-slot char-table n
1397 This function returns the contents of extra slot @var{n} (zero based)
1398 of @var{char-table}. The number of extra slots in a char-table is
1399 determined by its subtype.
1402 @defun set-char-table-extra-slot char-table n value
1403 This function stores @var{value} in extra slot @var{n} (zero based) of
1407 A char-table can specify an element value for a single character code;
1408 it can also specify a value for an entire character set.
1410 @defun char-table-range char-table range
1411 This returns the value specified in @var{char-table} for a range of
1412 characters @var{range}. Here are the possibilities for @var{range}:
1416 Refers to the default value.
1419 Refers to the element for character @var{char}
1420 (supposing @var{char} is a valid character code).
1422 @item @code{(@var{from} . @var{to})}
1423 A cons cell refers to all the characters in the inclusive range
1424 @samp{[@var{from}..@var{to}]}.
1428 @defun set-char-table-range char-table range value
1429 This function sets the value in @var{char-table} for a range of
1430 characters @var{range}. Here are the possibilities for @var{range}:
1434 Refers to the default value.
1437 Refers to the whole range of character codes.
1440 Refers to the element for character @var{char}
1441 (supposing @var{char} is a valid character code).
1443 @item @code{(@var{from} . @var{to})}
1444 A cons cell refers to all the characters in the inclusive range
1445 @samp{[@var{from}..@var{to}]}.
1449 @defun map-char-table function char-table
1450 This function calls its argument @var{function} for each element of
1451 @var{char-table} that has a non-@code{nil} value. The call to
1452 @var{function} is with two arguments, a key and a value. The key
1453 is a possible @var{range} argument for @code{char-table-range}---either
1454 a valid character or a cons cell @code{(@var{from} . @var{to})},
1455 specifying a range of characters that share the same value. The value is
1456 what @code{(char-table-range @var{char-table} @var{key})} returns.
1458 Overall, the key-value pairs passed to @var{function} describe all the
1459 values stored in @var{char-table}.
1461 The return value is always @code{nil}; to make calls to
1462 @code{map-char-table} useful, @var{function} should have side effects.
1463 For example, here is how to examine the elements of the syntax table:
1468 #'(lambda (key value)
1472 (list (car key) (cdr key))
1479 (((2597602 4194303) (2)) ((2597523 2597601) (3))
1480 ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))
1481 ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
1486 @section Bool-vectors
1487 @cindex Bool-vectors
1489 A bool-vector is much like a vector, except that it stores only the
1490 values @code{t} and @code{nil}. If you try to store any non-@code{nil}
1491 value into an element of the bool-vector, the effect is to store
1492 @code{t} there. As with all arrays, bool-vector indices start from 0,
1493 and the length cannot be changed once the bool-vector is created.
1494 Bool-vectors are constants when evaluated.
1496 Several functions work specifically with bool-vectors; aside
1497 from that, you manipulate them with same functions used for other kinds
1500 @defun make-bool-vector length initial
1501 Return a new bool-vector of @var{length} elements,
1502 each one initialized to @var{initial}.
1505 @defun bool-vector &rest objects
1506 This function creates and returns a bool-vector whose elements are the
1507 arguments, @var{objects}.
1510 @defun bool-vector-p object
1511 This returns @code{t} if @var{object} is a bool-vector,
1512 and @code{nil} otherwise.
1515 There are also some bool-vector set operation functions, described below:
1517 @defun bool-vector-exclusive-or a b &optional c
1518 Return @dfn{bitwise exclusive or} of bool vectors @var{a} and @var{b}.
1519 If optional argument @var{c} is given, the result of this operation is
1520 stored into @var{c}. All arguments should be bool vectors of the same length.
1523 @defun bool-vector-union a b &optional c
1524 Return @dfn{bitwise or} of bool vectors @var{a} and @var{b}. If
1525 optional argument @var{c} is given, the result of this operation is
1526 stored into @var{c}. All arguments should be bool vectors of the same length.
1529 @defun bool-vector-intersection a b &optional c
1530 Return @dfn{bitwise and} of bool vectors @var{a} and @var{b}. If
1531 optional argument @var{c} is given, the result of this operation is
1532 stored into @var{c}. All arguments should be bool vectors of the same length.
1535 @defun bool-vector-set-difference a b &optional c
1536 Return @dfn{set difference} of bool vectors @var{a} and @var{b}. If
1537 optional argument @var{c} is given, the result of this operation is
1538 stored into @var{c}. All arguments should be bool vectors of the same length.
1541 @defun bool-vector-not a &optional b
1542 Return @dfn{set complement} of bool vector @var{a}. If optional
1543 argument @var{b} is given, the result of this operation is stored into
1544 @var{b}. All arguments should be bool vectors of the same length.
1547 @defun bool-vector-subsetp a b
1548 Return @code{t} if every @code{t} value in @var{a} is also t in
1549 @var{b}, @code{nil} otherwise. All arguments should be bool vectors of the
1553 @defun bool-vector-count-consecutive a b i
1554 Return the number of consecutive elements in @var{a} equal @var{b}
1555 starting at @var{i}. @code{a} is a bool vector, @var{b} is @code{t}
1556 or @code{nil}, and @var{i} is an index into @code{a}.
1559 @defun bool-vector-count-population a
1560 Return the number of elements that are @code{t} in bool vector @var{a}.
1563 The printed form represents up to 8 boolean values as a single
1568 (bool-vector t nil t nil)
1575 You can use @code{vconcat} to print a bool-vector like other vectors:
1579 (vconcat (bool-vector nil t nil t))
1580 @result{} [nil t nil t]
1584 Here is another example of creating, examining, and updating a
1588 (setq bv (make-bool-vector 5 t))
1599 These results make sense because the binary codes for control-_ and
1600 control-W are 11111 and 10111, respectively.
1603 @section Managing a Fixed-Size Ring of Objects
1605 @cindex ring data structure
1606 A @dfn{ring} is a fixed-size data structure that supports insertion,
1607 deletion, rotation, and modulo-indexed reference and traversal. An
1608 efficient ring data structure is implemented by the @code{ring}
1609 package. It provides the functions listed in this section.
1611 Note that several rings in Emacs, like the kill ring and the
1612 mark ring, are actually implemented as simple lists, @emph{not} using
1613 the @code{ring} package; thus the following functions won't work on
1616 @defun make-ring size
1617 This returns a new ring capable of holding @var{size} objects.
1618 @var{size} should be an integer.
1621 @defun ring-p object
1622 This returns @code{t} if @var{object} is a ring, @code{nil} otherwise.
1625 @defun ring-size ring
1626 This returns the maximum capacity of the @var{ring}.
1629 @defun ring-length ring
1630 This returns the number of objects that @var{ring} currently contains.
1631 The value will never exceed that returned by @code{ring-size}.
1634 @defun ring-elements ring
1635 This returns a list of the objects in @var{ring}, in order, newest first.
1638 @defun ring-copy ring
1639 This returns a new ring which is a copy of @var{ring}.
1640 The new ring contains the same (@code{eq}) objects as @var{ring}.
1643 @defun ring-empty-p ring
1644 This returns @code{t} if @var{ring} is empty, @code{nil} otherwise.
1647 The newest element in the ring always has index 0. Higher indices
1648 correspond to older elements. Indices are computed modulo the ring
1649 length. Index @minus{}1 corresponds to the oldest element, @minus{}2
1650 to the next-oldest, and so forth.
1652 @defun ring-ref ring index
1653 This returns the object in @var{ring} found at index @var{index}.
1654 @var{index} may be negative or greater than the ring length. If
1655 @var{ring} is empty, @code{ring-ref} signals an error.
1658 @defun ring-insert ring object
1659 This inserts @var{object} into @var{ring}, making it the newest
1660 element, and returns @var{object}.
1662 If the ring is full, insertion removes the oldest element to
1663 make room for the new element.
1666 @defun ring-remove ring &optional index
1667 Remove an object from @var{ring}, and return that object. The
1668 argument @var{index} specifies which item to remove; if it is
1669 @code{nil}, that means to remove the oldest item. If @var{ring} is
1670 empty, @code{ring-remove} signals an error.
1673 @defun ring-insert-at-beginning ring object
1674 This inserts @var{object} into @var{ring}, treating it as the oldest
1675 element. The return value is not significant.
1677 If the ring is full, this function removes the newest element to make
1678 room for the inserted element.
1681 @cindex fifo data structure
1682 If you are careful not to exceed the ring size, you can
1683 use the ring as a first-in-first-out queue. For example:
1686 (let ((fifo (make-ring 5)))
1687 (mapc (lambda (obj) (ring-insert fifo obj))
1689 (list (ring-remove fifo) t
1690 (ring-remove fifo) t
1691 (ring-remove fifo)))
1692 @result{} (0 t one t "two")