| % File src/library/stats/man/zC.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2007 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{C} |
| \title{Sets Contrasts for a Factor} |
| \usage{ |
| C(object, contr, how.many, \dots) |
| } |
| \alias{C} |
| \arguments{ |
| \item{object}{a factor or ordered factor} |
| \item{contr}{which contrasts to use. Can be a matrix with one row for |
| each level of the factor or a suitable function like |
| \code{contr.poly} or a character string giving the name of the function} |
| \item{how.many}{the number of contrasts to set, by default one less |
| than \code{nlevels(object)}.} |
| \item{\dots}{additional arguments for the function \code{contr}.} |
| } |
| \description{ |
| Sets the \code{"contrasts"} attribute for the factor. |
| } |
| \details{ |
| For compatibility with S, \code{contr} can be \code{treatment}, |
| \code{helmert}, \code{sum} or \code{poly} (without quotes) as shorthand |
| for \code{contr.treatment} and so on. |
| } |
| \value{ |
| The factor \code{object} with the \code{"contrasts"} attribute set. |
| } |
| \seealso{ |
| \code{\link{contrasts}}, \code{\link{contr.sum}}, etc. |
| } |
| \references{ |
| Chambers, J. M. and Hastie, T. J. (1992) |
| \emph{Statistical models.} |
| Chapter 2 of \emph{Statistical Models in S} |
| eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole. |
| } |
| \examples{ |
| ## reset contrasts to defaults |
| options(contrasts = c("contr.treatment", "contr.poly")) |
| tens <- with(warpbreaks, C(tension, poly, 1)) |
| \donttest{attributes(tens)} |
| ## 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) |
| } |
| \keyword{models} |