[Qgis-user] model builder - merge several inputs

[Simon Dietmann]

Hi Nicolas,
 
thank you for your quick reply. I am not sure if I understand correctly what you are suggesting, because the ‘join by attribute’ and ‘aggregate’ functions both will change the attributes of the vector layer. 
 
What I´m trying to do instead is to give a list of field names as a parameter to the function ‘statistics by categories’, and my problem is that I don´t have this single list, but two separate lists that each contain a part of these field names. So I would like to merge the two lists of field names and pass it over to the algorithm, but I have no idea how to do this.
 
Another solution could be to perform the ‘union’ first, and only afterwards ask the user to specify the field names for evaluation. Unfortunately, I have no idea either how to determine a chronological sequence where the ‘vector field’ input is queried after the ‘union’ has already been performed.
 
Thank you very much for your help, 


Simon 
 
Von: Nicolas Cadieux <njacadieux.gitlab at gmail.com> 
Gesendet: Mittwoch, 26. Januar 2022 17:21
An: Simon Dietmann <simon.dietmann at pgnu.de>; qgis-user at lists.osgeo.org
Betreff: Re: [Qgis-user] model builder - merge several inputs
 
Hi,
You could try a "join attribute by location" followed by a "Aggregate"...
Nicolas
On 2022-01-26 3:43 a.m., Simon Dietmann wrote:
Dear list,
 
I am trying to find a solution for the following problem with the model builder:
 
My model asks for two vector polygon layers that will be combined by ‘union’. The resulting layer gets a new field (field calculator) and is evaluated by ‘Statistics by categories’ algorithm. The fields for the categories are selected by the user when calling the model. Since those fields are present in the two separate input layers, I have to use two separate ‘Vector field’ inputs.
The problem arises when I try to combine those two input variables to use them together for the ‘Statistics by categories’ algorithm. AFAICS there is no function inside the model builder to achieve this, so I suggest I have to export the model as  a python script. There I found that the call of the Statistics function gives the name of the variable as a parameter and not the variable itself:
alg_params = {
            'CATEGORIES_FIELD_NAME': parameters['fields'], ….
 
How can I combine my two lists (~like “parameters[‘fields’+’fields2’], or is there a way to do this inside the model builder that I didn´t find?
Thanks in advance for help, kind regards
 
Simon Dietmann
 
 
 


Mit freundlichen Grüßen
im Auftrag

Simon Dietmann
M.Sc. Physische Geografie
 
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