C {base} | 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.
B.D. Ripley
## 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)