Found the "Delete All" command.
Here is a script that illustrates how to do that:
Names Default To Here( 1 ); dt = Open( "$SAMPLE_DATA/Big Class.jmp" ); df = dt << Data Filter( add filter( columns( :sex ) ) ); Wait( 5 ); df << delete all;
All of the capabilities of the Data Filter are available from:
Help==Scripting Index==>Data Table Rows==>Data Filter