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From: Carsten Dominik <dominik@uva.nl>
To: Nicolas Goaziou <n.goaziou@neuf.fr>
Cc: emacs-orgmode@gnu.org
Subject: Re: Spreadsheet and weighted means
Date: Mon, 29 Sep 2008 10:43:14 +0200	[thread overview]
Message-ID: <9136F031-BBCD-4A80-A117-6047C5D3F777@uva.nl> (raw)
In-Reply-To: <87wsh7w589.fsf@selenimh.orion.org>


On Sep 20, 2008, at 9:00 AM, Nicolas Goaziou wrote:

> Hello,
>
> I stumbled upon this problem : I'd like to compute the weighted mean  
> of
> some values, even though cells might be empty. In fact, I'm aiming at
> something like this :
>
> |           | Coeff. |    0.2 |    0.5 |      1 |
> |-----------+--------+--------+--------+--------|
> | Name      |   Mean | Test 1 | Test 2 | Test 3 |
> |-----------+--------+--------+--------+--------|
> | Student A |     10 |     15 |     12 |      8 |
> | Student B |     12 |        |     16 |     10 |
>
> where 10=(15*0.2+12*0.5+8*1)/(0.2+0.5+1) and 12=(16*0.5+10*1)/(0.5+1)
>
> I just can't guess what has to be put in @3$2 as a column formula to
> calculate those mean means… I perhaps have overlooked something  
> simple.
> Anyway, if anyone has a clue here, I will be pleased to hear it.

Hi Nicolas, there s no builtin way to deal with this, in particular  
with the fact that you want to treat empty fields as non-existing, and  
therefore also to ignore the corresponding weight.

You cou write a Lisp function to do this, though:

(defun my-wmean (values weights)
   (let ((vsum 0) (wsum 0))
     (while (and values weights)
       (setq v (pop values) w (pop weights))
       (unless (equal "" v)
	(setq vsum (+ vsum (* (string-to-number w) (string-to-number v)))
	      wsum (+ wsum (string-to-number w)))))
     (/ vsum wsum)))


The you could use this as your equation:

|           | Coeff. |    0.2 |    0.5 |      1 |
|-----------+--------+--------+--------+--------|
| Name      |      0 | Test 1 | Test 2 | Test 3 |
|-----------+--------+--------+--------+--------|
| Student A |     10 |     15 |     12 |      8 |
| Student B |     12 |        |     16 |     10 |
#+TBLFM: $2='(wmean '($3..$5) '(@1$3..@1$5));E%d


Note the use of the E flag, to make sure empty fields are not skipped,  
but passed through as empty strings.......

Hope this helps.

- Carsten





>
>
> -- 
> Nicolas Goaziou
>
>
> _______________________________________________
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> Emacs-orgmode@gnu.org
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  reply	other threads:[~2008-09-29  8:55 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-09-20  7:00 Spreadsheet and weighted means Nicolas Goaziou
2008-09-29  8:43 ` Carsten Dominik [this message]
2008-09-29  8:44   ` Carsten Dominik
2008-10-01 16:46   ` Nicolas Goaziou
2008-10-01 19:26     ` Carsten Dominik
2008-10-01 19:45       ` Embedded elisp formulas, was: " Eric Schulte
2008-10-01 20:29         ` Paul R
2008-10-02  0:03           ` Eric Schulte
2008-10-02 11:44             ` Carsten Dominik
2008-10-08 23:12               ` ANN: org-eval-light.el was: " Eric Schulte
2008-11-06  1:19               ` Eric Schulte
2008-11-09  7:02                 ` Carsten Dominik
2008-11-10 19:51                   ` Daniel Clemente
2008-10-04  8:49       ` Nicolas Goaziou

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