ids is a string array like ["id_1", "id_2", ...] and letters is a
parallel string array like ["A", "B", "C", ...]. Return a 2-column integer array
where column 0 is ids with the "id_" characters stripped and converted to int,
and column 1 is letters mapped A→1, B→2, C→3, D→4, E→5, F→6.
Input
ids = ['id_1' 'id_2' 'id_3']
letters = ['B' 'A' 'C']
Output
[[1 2]
[2 1]
[3 3]]