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From: "WJ" <w_a_x_...@yahoo.com>
Newsgroups: comp.lang.lisp
Subject: Re: how to split by half?
Date: 6 Mar 2011 22:12:15 GMT
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Tamas K Papp wrote:

> On Tue, 07 Dec 2010 03:10:11 -0800, Steve wrote:
> 
> > I'm learning CLISP, and i would to know if there's a function (or how to
> > defun'e) that given a sequence (list, array, string...) split it by
> > half+1, Something like this;
> > 
> > (split-by-half '(a b c d e f g))
> > 
> > must returns:
> > 
> > (a b c d)
> > 
> > then assign the half+1 part to a list and the other half to another
> > list.
> 
> (defun split-in-half (sequence)
>   (let ((mid (ceiling (length sequence) 2)))
>     (values (subseq sequence 0 mid)
>             (subseq sequence mid nil))))
> 
> Returns the two sequences as two values.  See MULTIPLE-VALUE-BIND on
> how to make use of both returned values.  If you want a list of lists,
> replace VALUES by LIST.
> 

Guile Scheme:

(define (split-in-half seq)
  (let ((n (ceiling (/ (length seq) 2))))
    (split-at seq n)))