An index function for strings in emacs-lisp

Posted March 05, 2013 at 07:28 PM | categories: emacs-lisp | tags:

Updated March 05, 2013 at 07:28 PM

I could not find an index function for strings in emacs-lisp. The position function seems to work for numbers, but not strings. Here is a version that works on strings. 

(defun index (item list)
  "return index of item in list or nil"
  (let ((counter 0)
        (found nil))
    (dolist (listelement list counter)
      (if (string= item listelement)
        (progn 
          (setq found t)
          (return counter)) ; exit the loop
        ;; else increment counter
        (incf counter)))
    ;; if we found it return counter otherwise return nil
    (if found counter nil)))

index

Here are some example uses: 

(index "test" '("a" "test" "y"))

1

(index "z" '("a" "b" "z"))

2

(index "testy" '("a" "test" "y"))

nil

This raises an error because we use string=. 

(index 1 '("a" "test" "y" 1))

Copyright (C) 2013 by John Kitchin. See the License for information about copying.

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