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")) 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)) # following on from help(esoph) model3 <- glm(cbind(ncases, ncontrols) ~ agegp + C(tobgp, , 1) + C(alcgp, , 1), data = esoph, family = binomial()) summary(model3)