[Qgis-user] Reclassify field values from txt rule file in QGIS

[Andrea Giudiceandrea]

> fabio castelli fabio.castelli92 at outlook.it
> Wed Jun 28 05:52:45 PDT 2023

> I kindly ask for your support with an issue related to the reclassification of attribute tables with the v.reclass function.
> Here's the link to the question posted on Stackexchenge: https://gis.stackexchange.com/questions/462318/reclassify-field-values-from-txt-rule-file-in-qgis

Hi Fabio,
looking at your question posted on Stackexchenge, the error message 
("Either 'rules' or 'column' must be specified") is very clear and it is 
due to the fact the you have specified both the "rules" and "column" 
parameters instead of only one of them.

Anyway, it looks like it is actually incorrectly impossible to specify 
only the "rules" parameter in the QGIS processing algorithm GUI for the 
v.reclass GRASS-GIS module without also specifying the "column" 
parameter: this is due to the fact that the "column" parameter is 
incorrectly flagged as mandatory instead of optional.

You can workaround this issue editing the v.reclass.txt file in the 
folder with path [QGIS installation 
dir]\apps\qgis\python\plugins\grassprovider\description\ or [QGIS 
installation 
dir]\apps\qgis-ltr\python\plugins\grassprovider\description\ (provided 
you are using QGIS 3.32 or QGIS LTR 3.28 on Windows) and to change the 
the sixth line from:

QgsProcessingParameterField|column|The name of the column whose values 
are to be used as new categories|None|input|-1|False|False

to:

QgsProcessingParameterField|column|The name of the column whose values 
are to be used as new categories|None|input|-1|False|True


I also suggest you to read the v.reclass GRASS-GIS module manual 
available at https://grass.osgeo.org/grass82/manuals/v.reclass.html in 
order to better understand what the "rules" file must contains.


Best regards.

Andrea Giudiceandrea