Calculating field with input from two layers in QGIS Graphical Modeler

Question

Even though I found similar questions, I couldn't find a suitable answer for the problem I have.

I want to create a model that calculates the difference between two fields ("NUMPOINTS") from different vector files and populate a new field with the result in a new vector file.

My input are 2 vector layers: 'Events A' and 'Events B'. These tables have the same fields, including a common "id" field.

I need to create a 'Table C' where "DIFFERENCE" field is calculated as follow: "NUMPOINTS" ('Table B') - "NUMPOINTS" ('Table A')

So far, I managed to create a Join, but I don't know how to create a new field with input from the two input files.

enter image description here

Answer 1

you can use the fieldcalculator in your model to do the calculation:

enter image description here

since your fields have the same name "NUMPOINTS" you can use a prefix for the joind NUMPOINTS field in the JOIN operation:

enter image description here

the formula in the fieldcalculator would be:

enter image description here

• eurojam: if this answer is a solution to your question you can mark the answer as accepted...