Re: Partition for Emacs Lisp

[Marc Tfardy]

Pascal J. Bourguignon schrieb:
> Marc Tfardy <bum@cyk.cyk> writes:
>
> > Hi!
> >
> > I looking for a ELISP function that do the job like Partition in
> > Mathematica. The simplest case:
> >
> > (partition '(a b c d e f) 2)
> > should return:
> > ((a b) (c d) (e f))
>
> (defun partition-list (list length)
>   (loop
>      while list
>      collect (subseq list 0 length)
>      do (setf list (nthcdr length list))))
>
> (defun partition-vector (vector length)
>   (loop
>      for i = 0 then (+ i length)
>      while (< i (length vector))
>      collect (subseq vector i (+ i length))))
>      
> (defun partition (sequence length)
>    (etypecase sequence
>       (list   (partition-list sequence length))
>       (string (partition-vector sequence length)) ; emacs lisp strings are not vectors! 
>       (vector (partition-vector sequence length))))

Is there some reason (performance?) to write partition as above
and not as:

(defun partition (sequence length)
  (cond ((listp sequence)
         (partition-list sequence length))
        ((stringp sequence)
         (partition-vector sequence length)) ; emacs lisp strings are not 
vectors!
        ((vectorp sequence)
          (partition-vector sequence length))))


regards
Marc