Re: how to clear computed values

[Cecil Westerhof <CecilWesterhof@xs4all.nl>]

Op wo, 11-07-2007 te 08:15 +0200, schreef Carsten Dominik:
> If you want to understand why things come out the way they
> do, use formular debugging (this is an option in the menu, but
> cou can also toggle it with `C-C {').  When you then execute
> calculations in the table (for example with `C-u C-c C-c')
> you will get detailed information about variable substitution,
> and you will see the final expression that gets evaluated.

That is a good tip. ;-}


> For example, you are trying things like
> 
>    (and $1 $2 ...
> 
> but of course both the empty string and the number 0 are
> "true" in Lisp, the only thing false in Lisp is "nil".

That explains my problems.


> If you want to fix it, you can, by *really* taking control.
> For example, define the following function that tests
> if a value is not zero
> 
> (defun nz (n) (not (= n 0.)))
> 
> and then write your table like this:
> 
>    |---------+------+---------+--------+-------+----------+--------|
>    | kmstand | km's | prijs/l | liters | prijs | prijs/km |   km/l |
>    |---------+------+---------+--------+-------+----------+--------|
>    |  155111 |      |         |        |       |          |        |
>    |  156146 | 1035 |   102.2 |  62.25 | 63.62 |    6.147 | 16.627 |
>    |         |      |         |        |       |          |        |
>    |---------+------+---------+--------+-------+----------+--------|
> #+TBLFM: $2='(if (and (nz @-1$-1) (nz $1) (> $1 @-1$-1)) (- $1 @-1$-1) 
> "");N::$5='(if (and (nz $3) (nz $4)) (format "%.2f" (/ (* $3 $4) 100)) 
> "");N::$6='(if (and (nz $2) (nz $5)) (format "%.3f" (/ (* $5 100) $2)) 
> "");N::$7='(if (and (nz $2) (nz $4)) (format "%.3f" (/ $2 $4)) "");N

That works perfect.


> Yes, those equations look longish - use the formula
> editor to edit them.

That is also a nice tool yes.


> Also, consider to put the "#" marker in the first column,
> to get this table to recompute automatically while
> you step through with TAB.  Use C-# in the first data line
> to insert the "#" if you want to make sure that your
> existing formulas are modified to reflect the new
> column numbers.  The result will be this:

That is also very usefull.


> Hope this helps.

It certainly did.

I made another improvement. It would be nice to have a notification when
there is a problem with kmstand.
I made the folowing:
        |---+------------+---------+-------------------+---------+--------+-------+----------+--------|
        |   |      datum | kmstand | km's              | prijs/l | liters | prijs | prijs/km |   km/l |
        |---+------------+---------+-------------------+---------+--------+-------+----------+--------|
        | # |            |  155111 | Verkeerde kmstand |         |        |       |          |        |
        | # | 2007-07-09 |  156146 | 1035              |   102.2 |  62.25 | 63.62 |    6.147 | 16.627 |
        | # |            |    6953 | Verkeerde kmstand |         |        |       |          |        |
        | # |            |         |                   |         |        |       |          |        |
        |---+------------+---------+-------------------+---------+--------+-------+----------+--------|
        #+TBLFM: $4='(if (and (nz @-1$3) (nz $3)) (if (> $3 @-1$3) (- $3 @-1$3) "Verkeerde kmstand") "");N::$7='(if (and (nz $5) (nz $6)) (format "%.2f" (/ (* $5 $6) 100)) "");N::$8='(if (and (nz $4) (nz $7)) (format "%.3f" (/ (* $7 100) $4)) "");N::$9='(if (and (nz $4) (nz $6)) (format "%.3f" (/ $4 $6)) "");N
In this example the first two digits of kmstand where not input at row 3
and you get a message. But you get also a message at the first row. Is
it possible to circumvent this?

Is it possible to define functions in an org-file? For example: it would
be nice to have more extensive checking on the values. Also the nz could
be defined. It is in my .emacs now, but when I transfer the file to
another computer, there is a risk that it doe not work anymore.

It would be nice if I did input kmstand that with tab you go to prijs/l.
(Skipping fields with formula's.) And when giving tab on the field
liters going to the field kmstand. Is that something that could be made?

-- 
Cecil Westerhof <CecilWesterhof@xs4all.nl>