char-occurrences-in-string.el

;; http://emacs.1067599.n5.nabble.com/How-to-count-the-number-of-occurrences-of-a-character-in-a-string-td371732.html
;; https://gist.github.com/joostkremers/0e07a35c85758a2fcb52

(defvar num-repeats 100000)

(defun count-char-in-string-cl-count (char str)
  (cl-count char str))

(defun count-char-in-string-mapcar (char str)
  (apply '+ (mapcar (lambda (x) (if (= x char) 1 0))
                    str)))

(defun count-char-in-string-mapc (char str)
  (let ((num-matches 0))
    (mapc (lambda (ascii)
            (when (eq char ascii)
              (setq num-matches (1+ num-matches))))
          (append str nil))
    num-matches))

(defun count-char-in-string-cdr (char str)
  (let ((str-list (append str nil))
        (num-matches 0))
    (while str-list
      (if (= (car str-list) char)
          (setq num-matches (1+ num-matches)))
      (setq str-list (cdr str-list)))
    num-matches))

;; (defun count-char-in-string-split-string (char str)
;;   (let ((c (concat "[" (regexp-quote (char-to-string char)) "]")))
;;     (length (split-string c str t))))

(defun count-char-in-string-aref (char str)
  (let ((count 0)
        (end (length str))
        (i 0)
        x)
    (while (< i end)
      (setq x (aref str i))
      (if (eq char x)
          (setq count (1+ count)))
      (setq i (1+ i)))
    count))

(defun count-char-in-string-string-match (char str)
  "Count the number of times CHAR character appears in STR string."
  ;; (message "\n==========\nstr = %0s" str)
  (let* ((num-matches 0)
         (ptr 0) ; initiate pointer for string match
         match-pos)
    (while (<= ptr (length str))
      ;; (message "ptr = %0d" ptr)
      (setq match-pos (string-match-p
                       (regexp-quote (char-to-string char)) str ptr))
      (if match-pos
          (progn
            (setq ptr (1+ match-pos))
            ;; (message "match-pos = %0d ptr = %0d" match-pos ptr)
            (setq num-matches (1+ num-matches)))
        (progn
          (setq ptr (1+ (length str))))))
    ;; (message "%0d occurrence%0s of `%c' char found in \"%s\"."
    ;;          num-matches (if (/= 1 num-matches) "s" "") char str)
    num-matches))

(defun count-char-in-string-test (fn)
  (let ((bm-result (benchmark num-repeats
                              '(progn
                                 (funcall fn ?a "abcda")
                                 (funcall fn ?z "abcda")
                                 (funcall fn ?f "falalala")
                                 (funcall fn ?l "falalalaabcds")
                                 (funcall fn ?^ "f^la^lala^dabra^^")
                                 (funcall fn ?\\ "\\falalala\\")))))
    (list fn bm-result)))

(defun count-char-in-string-run-tests ()
  (insert "\n")
  (mapc (lambda (fn)
          (let ((res (count-char-in-string-test fn)))
            (insert (format ";; %-35s %s\n" (car res) (cadr res)))))
        '(cl-count
          count-char-in-string-aref
          count-char-in-string-cl-count
          count-char-in-string-mapcar
          count-char-in-string-mapc
          count-char-in-string-cdr
          count-char-in-string-string-match))
  (insert "\n"))

(count-char-in-string-run-tests)

;; cl-count                            Elapsed time: 1.540646s
;; count-char-in-string-aref           Elapsed time: 1.794012s
;; count-char-in-string-cl-count       Elapsed time: 1.133700s
;; count-char-in-string-mapcar         Elapsed time: 2.033713s (1.163422s in 8 GCs)
;; count-char-in-string-mapc           Elapsed time: 2.140363s (1.170861s in 8 GCs)
;; count-char-in-string-cdr            Elapsed time: 2.543917s (1.168051s in 8 GCs)
;; count-char-in-string-string-match   Elapsed time: 4.002969s (2.516860s in 17 GCs)