Try this
dt = current data table();
dt << New Column( "MinCpk", numeric, formula(Col Minimum( :Cpk, :TestName )));
dt << select where(:Cpk > :MinCpk);
dt << delete rows;
dt << delete Column("MinCpk");
//___________________________________________________________
//or use this to keep the original table and create a new table with only the rows of interest
dt = Current Data Table();
dt << New Column( "MinCpk", numeric, formula( Col Minimum( :Cpk, :TestName ) ) );
idx = dt << get rows where( :Cpk == :MinCpk );
newtbl = dt << subset( Rows( idx ), All Columns, Output Table Name( "Table2" ) );
newtbl << delete columns( "MinCpk" );