Get incorrect index list

Hi all,
I try to filter some wall by Vector.Y with List.GroupByFunction, as a result List.IndexOf should be ascending but it don’t ( with incorrect sequence ).
For clarifications see the attached snip.

Please suggest how to get List.IndexOf result as a ascending sequence.

Thank You

Try using sort by key node and the key here will be Vector.Y it will sort the key then sort the original list.