[Qgis-user] Field calculator QGIS2.4 division error

[Siki Zoltan]

Dear Ivan,

it is not strange, c/c++ evaluate expressions this way.
100.0 * "HC01_VC04"  /  "HC01_VC03" will give you the right result.
First the multiplication is evaluated (left to right rule), the result is 
float, then float over integer gives float result.
/ is really two operators, integer division and float division.
If both operands are integer then integer division is used.

Cheers,
Zoltan

On Fri, 22 Aug 2014, Ivan Santiago wrote:

> Hello all:
> Thanks Ralf.
> The columns used are integer. The resulting column is real, lenght=10 precision=1
>
> Writing "HC01_VC04"  /  "HC01_VC03" * 100.0
> Does not work either.
>
> Applying convert function toreal() to one of the columns, produces correct results. I checked it against LibreOffice Calc.
>
> BTW:
> The calculator has a strange behavior though. I need to sort and sort again the calculated column to 'refresh' the table values.
>
> QGIS 2.4 32bit under WIN7.
>
> ---------------------------
> Iván Santiago
> GIS Specialist
> Information Technologies
> Office of Management and Budget
> 787.725.9420 x 2378
> Calle Cruz 254
> PO Box 9023228
> San Juan, PR 00902-3228
> http://gis.pr.gov<http://gis.pr.gov/>
>
> From: Ivan Santiago
> Sent: Thursday, August 21, 2014 4:04 PM
> To: 'qgis-user at lists.osgeo.org'
> Subject: RE: Field calculator QGIS2.4 division error
>
> Hello all:
>
> Does anyone have had problems with field calculations using the division operator?
>
> I've tried many times to update a new field using both the old field calculator and the new interface but they just don't work with division.
>
> Simple operations like:
> "HC01_VC04"  /  "HC01_VC03" * 100
> Do not work.
> The  only workaround I found was to put the function abs into the denominator:
> "HC01_VC04"  /  abs("HC01_VC03") * 100
>
> Then it gives the result but this should be avoidable.
>
> I'll send the table used if anyone want to try it.
>
> Qgis version is 2.4 (32bit) under WIN7.
>
> ---------------------------
> Iván Santiago
> GIS Specialist
> Information Technologies
> Office of Management and Budget
> 787.725.9420 x 2378
> Calle Cruz 254
> PO Box 9023228
> San Juan, PR 00902-3228
> http://gis.pr.gov<http://gis.pr.gov/>
>
>