From ...
Path: supernews.google.com!sn-xit-02!supernews.com!216.227.56.88.MISMATCH!telocity-west!TELOCITY!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!uio.no!Norway.EU.net!127.0.0.1!nobody
From: Erik Naggum <erik@naggum.net>
Newsgroups: comp.lang.lisp
Subject: Re: Q: total addition within an array. (any function or macro?)
Date: 15 Dec 2000 17:42:47 +0000
Organization: Naggum Software; vox: +47 800 35477; gsm: +47 93 256 360; fax: +47 93 270 868; http://naggum.no; http://naggum.net
Lines: 34
Message-ID: <3185890967472817@naggum.net>
References: <91dcr2$3n$1@nnrp1.deja.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: oslo-nntp.eunet.no 976904222 12481 195.0.192.66 (15 Dec 2000 18:17:02 GMT)
X-Complaints-To: newsmaster@eunet.no
NNTP-Posting-Date: 15 Dec 2000 18:17:02 GMT
mail-copies-to: never
User-Agent: Gnus/5.0803 (Gnus v5.8.3) Emacs/20.7
Xref: supernews.google.com comp.lang.lisp:5336

* sungwoo@cad.strath.ac.uk
| One condition is, I don't know the total length of an array because it
| will be changed every time.  Maybe I could write down as (although it
| looks complicated..),
| 
| (setf total-value 0)
| (loop for i from 0 to arr-index
|          do (setf total-value (+ total-value (aref arr i)))
|          finally (setf ave-value (/ total-value (+ arr-index 1))))
| 
| However, I just wonder that is there any function or macro which can
| add whole values in an array?  I want use this function with one
| simple line.... I couldn't find that kind of things, but maybe
| something exist? Thanks for advance. =)

  I should give you the hints and the pointers, but I'm tired, so here's
  how you compute the average of a vector of numbers:

              (/ (reduce #'+ <vector>) (length <vector>))

  Incidentally, the standard deviation is also very useful if you ever
  work with averages:

(let* ((mean (/ (reduce #'+ <vector>) (length <vector>)))
       (sdev (sqrt (/ (reduce #'+ <vector> :key #'(lambda (elt) (expt (- elt mean) 2)))
		      (1- (length <vector>))))))
  ...)

  As you may have noticed, this is idiomatic Common Lisp for the sum
  operator.

#:Erik
-- 
  The United States of America, soon a Bush league world power.  Yeee-haw!