QGIS Labeling expression to format a values list in a series of 2 columns of 2 records

Question

From a layer of overlapping points (identical coordinates) containing the field "RC", I'm using the following expression to make the label of unique values:

array_to_string(array_distinct(array_prepend(overlay_equals(@layer, "RC"), "RC")),'RC')

And to avoid duplicates I use the following expression in the labeling option 'Show label'.

$id=array_agg($id, "XCOORD"||"YCOORD")[0]

I would like, if possible, to reuse the labeling expression, to format the list of values to appear in a series of 2 columns of 2 records:

Simulation

Answer 1

I think the following approach could work:

with_variable(
'values', array_remove_all(array_distinct(array_prepend(overlay_equals(@layer, "RC"), "RC")), NULL),
with_variable(
    'num_values', array_length(@values),
    with_variable(
        'rows', ceil(@num_values / 2),
        with_variable(
            'labels', array_foreach(
                generate_series(0, @rows - 1),
                with_variable(
                    'row_index', @element * 2,
                    @values[@row_index] || ' ' || if(@num_values > @row_index + 1, @values[@row_index + 1], '')
                )
            ),
            array_to_string(@labels, '\n')
        )
    )
)

The "show label" expression you are using I think is fine.