[GRASS-user] Fwd: calculate values of an attribute table column

[Moritz Lennert]

On 21/10/08 14:23, Moritz Lennert wrote:
> On 21/10/08 13:23, G. Allegri wrote:
>> You could use v.db.update:
>> http://grass.osgeo.org/grass64/manuals/html64_user/v.db.update.html
>> In the qcolumn filed you can insert a formula
>>
>> As fas as I know, when using dbf tables you can't do calculations on
>> multiple fields (for a single column you can insert formulas inside
>> qcolumn in v.db.update). 
> 
> You can add, substract and multiply columns, but there seems to be a bug 
> for division. Will file a report.

Sorry, I take that back: division works, but the error you get in case 
of a division by 0 is a bit cryptic:

"ERREUR:This should not happen: got a wrong expression structure after
        parsing.
dbmi: Protocol error"

IIUC how the code is written, the "this should not happen" is not really 
precise. It will happen whenever you attempt a division by 0 or 
something similar...

Maybe it just needs a more user-friendly formulation.

Moritz