I have a vague recollection of seeing reference, fairly recently, to a function that forms a single factor which ``codes'' the interaction between two (or more?) factors. Do I recollect correctly? It would be easy enough to roll one's own, but if there is an existing function it probably does a much cleverer job than I would do. cheers, Rolf Turner rolf at math.unb.ca
Single factor from interaction.
2 messages · Rolf Turner, Chuck Cleland
Are you looking for interaction() ?
a <- gl(2, 4, 8)
b <- gl(2, 2, 8, label = c("ctrl", "treat"))
s <- gl(2, 1, 8, label = c("M", "F"))
interaction(a, b)
[1] 1.ctrl 1.ctrl 1.treat 1.treat 2.ctrl 2.ctrl 2.treat 2.treat
Levels: 1.ctrl 2.ctrl 1.treat 2.treat
interaction(a, b, s, sep = ":")
[1] 1:ctrl:M 1:ctrl:F 1:treat:M 1:treat:F 2:ctrl:M 2:ctrl:F
2:treat:M 2:treat:F
Levels: 1:ctrl:M 2:ctrl:M 1:treat:M 2:treat:M 1:ctrl:F 2:ctrl:F
1:treat:F 2:treat:F
Rolf Turner wrote:
I have a vague recollection of seeing reference, fairly recently, to a function that forms a single factor which ``codes'' the interaction between two (or more?) factors. Do I recollect correctly? It would be easy enough to roll one's own, but if there is an existing function it probably does a much cleverer job than I would do.
Chuck Cleland, Ph.D. NDRI, Inc. 71 West 23rd Street, 8th floor New York, NY 10010 tel: (212) 845-4495 (Tu, Th) tel: (732) 452-1424 (M, W, F) fax: (917) 438-0894