Can order change within the cell? And if there are no duplicates (such as row 4) is the " -" necessary?
Names Default To Here(1);
dt = New Table("Untitled",
	Compress File When Saved(1),
	New Column("Column 1",
		Character,
		"Nominal",
		Set Values({"a -a", "a - b", "a - c", "b - b", "b - c", "b - b", "b -"})
	)
);
dt << New Column("Column 2", Character, Nominal, << Set Each Value(
	Concat Items(Associative Array(Words(:Column 1, "- ")) << get keys, " - "));
);
					
				
			
			
				
	-Jarmo