L2 : Data manipulation

L2a:	Transform (search also classes L10a1, N6, and N8)	(1 routine)
L2b:	Tally	(5 routines)
L2c:	Subset	(1 routine)
L2d:	Merge (search also class N7)	(0 routines)
L2e:	Construct new variables (e.g., indicator variables)	(0 routines)