Expression Builder in QGIS in editing Attribute Table

Question

I am working with a simple attribute table that has 4 columns; 'Xcoord' 'Ycoord' 'id' 'id2'

'id2' is a new field that i added to the attribute table. 'id' is a field showing land use classes with values ranging from 0-210.

I wish to make 'id2' be filled up with new values ranging from 1-6, based on their value in the 'id' field.

For example, I wish to write an expression for;

when 'id' are values 10,20,30 and 40, i want them to have a value of 1 in 'id2' and 'id' values of 50,60,70 as 'id2' value of 2 and so on and so forth till an 'id2' value of 6.

Basically like a hierarchical aggregation of land cover classes.

I am trying to self-learn the QGIS expression builder but I am encountering many difficulties trying to code the expression properly.

Here is an image of the

Answer 1

You need to use Field calculator, select Update existing field and choose the correct field id2, and write the following expression, and:

Case
When "ID" in (10,20,30,40) then 1
When "ID" in (50,60,70) then 2
When "ID" in (#,#,#) then 3
end

where # is the other values, and repeat When statement to change values after then from 4 to 6