Counting number of points in one layer within fixed distance to points in another layer in QGIS

Question

In QGIS 3.22.7 I want to count the number of points on point 'layer B' within 60m of each point on point 'layer A' and add a column to the data on point 'layer A'. What is wrong with the following equation?

I couldn't get it to work by rewriting A into B. All the elements are zero. Or can I do it with the processing tool's functionality?

aggregate(
    'A', 
    'count',
    $id,
    filter:=distance(
        $geometry,
        geometry('B' )
        ) <= 60
    ) 

I am referring to this post: Counting points within certain distance of each other in QGIS

Answer 1

You must perform the calculation on layer A.
There are some problems with your expression:

1. The aggregate function allows to do some kind of a loop in the features of a layer, so you need to loop throw the objects of layer B filtering by distance. Some times this can looks confusing, because the field calculator is performing a loop and if you are using aggregates this will perform loops for every calculated feature.
2. When you use the filter in the aggregate function you can use the @parent variable to refer to the current object that's being calculated.

The correct expression is:

aggregate(
    layer:='B', -- here you loop throw the features of layer B
    aggregate:='count',
    expression:=$id,
    filter:=distance( -- this filter will be used to filter features of layer B
        $geometry, -- here $geometry refers to the geometry of layer B
        geometry(@parent) -- @parent is a variable containing the current feature that's being calculated of layer A
        ) <= 60
    ) 

Answer 2

Use this expression on layer A:

array_length(
    overlay_nearest (
        'B',
        $id,
        limit:=-1,
        max_distance:=60
    )
)

Blue points: layer B; red point: Layer A, labeled with the number of blue points within 60 meters, calculated with the expression above: