Programmatically selecting and deselecting rows in a tr:table with rowSelection="multiple"

[Yee, Richard K CTR DMDC]

Is it possible to programmatically select or deselect rows in a
tr:table? I would like to remove the rows that a user has selected from
within an action handler method that is bound to a commandButton.
It seems that when I call getSelectionState() on the CoreTable, I'm
getting a null RowKeySet.

Thanks,

Richard