[Trinidad] how to get tr:table rowKeys

[Renzo Tomaselli]

Hi, I used to manage tr:table through my own DataModel, which defines 
and returns rowKeys.
However, for simpler cases usually just a row array is enough, where row 
objects offer all field getters. Thus no special model is needed.
If I want to preselect some rows by means of the selectedRowKeys 
attribute, how do I get rowKeys from array elements/positions ?
Thanks,

-- Renzo