| C {stats} | R Documentation |
Sets the "contrasts" attribute for the factor.
C(object, contr, how.many, ...)
object |
a factor or ordered factor |
contr |
which contrasts to use. Can be a matrix with one row for
each level of the factor or a suitable function like
contr.poly or a character string giving the name of the function |
how.many |
the number of contrasts to set, by default one less
than nlevels(object). |
... |
additional arguments for the function contr. |
For compatibility with S, contr can be treatment,
helmert, sum or poly (without quotes) as shorthand
for contr.treatment and so on.
The factor object with the "contrasts" attribute set.
Chambers, J. M. and Hastie, T. J. (1992) Statistical models. Chapter 2 of Statistical Models in S eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.
## reset contrasts to defaults
options(contrasts=c("contr.treatment", "contr.poly"))
data(warpbreaks)
attach(warpbreaks)
tens <- C(tension, poly, 1)
attributes(tens)
detach()
## tension SHOULD be an ordered factor, but as it is not we can use
aov(breaks ~ wool + tens + tension, data=warpbreaks)
## show the use of ... The default contrast is contr.treatment here
summary(lm(breaks ~ wool + C(tension, base=2), data=warpbreaks))
data(esoph) # following on from help(esoph)
model3 <- glm(cbind(ncases, ncontrols) ~ agegp + C(tobgp, , 1) +
C(alcgp, , 1), data = esoph, family = binomial())
summary(model3)