Getting selected attributes from line layer to polygon layer in QGIS

Question

I am trying to get specific attributes from a line layer to a polygon layer. The line layer contains a number of pipes that run through a polygon (parcel). They both have the parcel number in common:

enter image description here

The darker the color, the more pipes are within that part of the line layer. I now want to transfer the HIGHEST number of pipes into the polygon layer. What I tried so far was "Join attribute by position" - which is kind of the tool I am looking for. However, this tool is either tranfering the attribute of the first line intersecting the polygon or the one with the most length in it. There is no way to add an expression that lets me filter for the most number of pipes. Any ideas?

• Taras: Try the following expression: overlay_contains(layer:='line_layer_name', expression:='needed_field_name', filter:=is_selected())
• ibdmn: I did not select anything, that is just my symbology (poor choice I guess). In this screenshot the orange line has a higher number as attribute than the yellow line. And that is the value that should be transfered to the polygon.

Answer 1

you should use the aggregate expression for that:

aggregate(layer:='line_layer',
 aggregate:= 'max',
 expression:="pipe_number_field_name",
 filter:=intersects($geometry,geometry(@parent)))

see also: https://docs.qgis.org/3.28/en/docs/user_manual/expressions/functions_list.html?highlight=aggregate#aggregate

• ibdmn: I think that's it. Was using aggregate before, but was missing the correct filter. Will do some tests but at the first look this is great!