QGIS expression - overlay function, using overlay function as filter

Question

I have a point layer with one field, id ranging from 0 to 9. I have a polygon that intersects some of the points, like so:

enter image description here

My aim is to use an expression to get the intersecting point with the highest value for id.

For demonstration purposes I use a Geometry Generator symbol layer on my polygon layer.

collect_geometries(
 overlay_intersects(
 'point_layer', 
 $geometry,
 filter:= id = array_max(overlay_intersects('point_layer', id))
 )
)

I expect there to be a single point at the location of the point in point_layer with the highest id (9). However, all intersecting points are returned.

enter image description here

When I test the expression I use for the filter as a standalone expression, it returns 9, as expected.

enter image description here

And when I hard-code the highest id value (9), I get the desired result:

collect_geometries(
 overlay_intersects(
 'point_layer', 
 $geometry,
 filter:= id = 9
 )
)

enter image description here

What am I missing?

Answer 1

Not a very elegant way, but I think it will work.

with_variable(
 'maxval',
 array_max(
 overlay_intersects(
 'point_layer', 
 "id"
 )
 ),
 array_filter(
 overlay_intersects(
 'point_layer', 
 array("id", $geometry)
 ),
 @element[0] = @maxval
 )[0][1]
)

• Matt: This seems like it should work, indeed. However, it is returning NULL. (Without the [0] array index it returns an empty array). That seems strange. Evaluating @maxval without the second overlay expression returns 9 as expected.
• Mayo: Ok, very strange behavior of this expression.
• Mayo: Just for debug, remove the filter from the second overlay. To see if it still return an empty array.
• Matt: Good idea to check. It's the expected array (using [0] gets the first point id=0).
• Mayo: So the problem is clearly the filter.