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A mapping function applies a given function to each element of a
list or other collection. Emacs Lisp has several such functions;
mapcar
and mapconcat
, which scan a list, are described
here. See Creating Symbols, for the function mapatoms
which
maps over the symbols in an obarray. See Hash Access, for the
function maphash
which maps over key/value associations in a
hash table.
These mapping functions do not allow char-tables because a char-table
is a sparse array whose nominal range of indices is very large. To map
over a char-table in a way that deals properly with its sparse nature,
use the function map-char-table
(see Char-Tables).
mapcar
applies function to each element of sequence in turn, and returns a list of the results.The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string. The result is always a list. The length of the result is the same as the length of sequence.
For example:
(mapcar 'car '((a b) (c d) (e f))) => (a c e) (mapcar '1+ [1 2 3]) => (2 3 4) (mapcar 'char-to-string "abc") => ("a" "b" "c") ;; Call each function inmy-hooks
. (mapcar 'funcall my-hooks) (defun mapcar* (function &rest args) "Apply FUNCTION to successive cars of all ARGS. Return the list of results." ;; If no list is exhausted, (if (not (memq 'nil args)) ;; apply function to cars. (cons (apply function (mapcar 'car args)) (apply 'mapcar* function ;; Recurse for rest of elements. (mapcar 'cdr args))))) (mapcar* 'cons '(a b c) '(1 2 3 4)) => ((a . 1) (b . 2) (c . 3))
mapc
is likemapcar
except that function is used for side-effects only—the values it returns are ignored, not collected into a list.mapc
always returns sequence.
mapconcat
applies function to each element of sequence: the results, which must be strings, are concatenated. Between each pair of result strings,mapconcat
inserts the string separator. Usually separator contains a space or comma or other suitable punctuation.The argument function must be a function that can take one argument and return a string. The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string.
(mapconcat 'symbol-name '(The cat in the hat) " ") => "The cat in the hat" (mapconcat (function (lambda (x) (format "%c" (1+ x)))) "HAL-8000" "") => "IBM.9111"