The subseq function lets you read from and write to specific portions
of a string (or any sequence, by I'm focusing on strings here):
(defparameter string (copy-seq "abcdefghijklmnopqrstuvwxyz"))
(subseq string 12)
=> "mnopqrstuvwxyz"
(subseq string 12 14)
=> "mn"
(setf (subseq string 24) "qwer")
string
=> "abcdefghijklmnopqrstuvwxqw" ; doesn't extend string
(setf (subseq string 22) "asdf")
=> "abcdefghijklmnopqrstuvasdf"
You can use mapcar to slice a string up by character:
(setf string "abcdefghijklmnopqrstuvwxyz")
(mapcar (lambda (i) (char string i))
'(3 4 5 12 0 2 17 14))
=> (#\d #\e #\f #\m #\a #\c #\r #\o)
(mapcar (lambda (i) (subseq string i (1+ i)))
'(3 4 5 12 0 2 17 14))
=> ("d" "e" "f" "m" "a" "c" "r" "o")
or by ofsets and lengths (this is vaguely similar to Perl's "unpack"
function):
(mapcar (lambda (i) (subseq string (first i) (+ (first i) (second i))))
'((4 2) (5 3) (6 4)))
=> ("ef" "fgh" "ghij")
(apply #'concatenate 'string
(mapcar (lambda (i) (subseq string (first i) (+ (first i) (second i))))
'((4 2) (5 3) (6 4))))
=> "effghghij"
Exchange the first and last characters in a string:
(defparameter string (copy-seq "make a hat"))
(rotatef (char string 0) (char string (1- (length string))))
string
=> "take a ham"
Just a few thoughts before bedtime. :) (Inspired by / adapted from
the Perl Cookbook, 1.1, "Accessing Substrings".)
-- Larry
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