QGIS count points layer to polygon layer that have the same field attribute

Question

From a layer with point geometry 'POINTS' and a layer with polygon geometry 'POLY'. Both layers have a common attribute field "UNIONCODE".

To the 'POINTS' layer I apply the following expression for Geometry Generator that draws a line to the center of the polygon with which it shares the same code 'UNIONCODE'.

make_line($geometry,point_on_surface(geometry(get_feature('POLY','UNIONCODE',attribute($currentfeature,'UNIONCODE')))))

enter image description here

To count the joining points that join each polygon with the shared attribute, I use the following expression:

aggregate(
 layer:='POINTS',
 aggregate:='count',
 expression:="UNIONCODE",
 filter:=intersects(
 make_line($geometry, point_on_surface(geometry(get_feature('POLY','UNIONCODE',attribute($currentfeature,'UNIONCODE'))))),
 $geometry
 )
)

enter image description here

As you can see, this expression only counts the total points and does not filter for each different polygon.

I would like to count the unions that are generated for each different polygon with an expression for Geometry Generator applicable to Labels.

Answer 1

As you already have an attribute that identifies the polygon each point is assigned to, you can count the points, grouped by this value - simply:

count (@id, group_by:=UNIONCODE)

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If you want to count based on the geometry (no. of points within each polygon), use this expression:

count (@id, group_by:=overlay_within ('POLY',@id)[0])