#CONTRASTS & LINEAR COMBINATIONS 

#TREATMENTS MODEL IN R
#READ STRUCTURED DATA TABLE WITH NUMERIC CODED FACTOR
K=read.table("c:/2008LinearModelsData/KentonFoodR.txt")
K
attach(K)

Y=Sales
X=factor(Design) # factor() IN DEFAULT SETTING

FM=lm(Y~X)
model.matrix(FM)
summary(FM)
anova(FM)

#CONSTRUCTING CELL MEANS MODEL IN R FROM factor()
contrasts(X,contrasts=F)
CM=lm(Y~X-1)  #FITS CELL MEANS MODEL
model.matrix(CM)
summary(CM)
Ys=scale(Y,scale=F)  #CENTER Y
CMs=lm(Ys~X)
anova(CMs)

#MAKING CONTRASTS IN R
require(gmodels)  #MUST LOAD {gmodels} PACKAGE FROM CRAN

#CONTRAST FOR KNNL P. 743
fit.contrast(FM,X,c(0.5,0.5,-0.5,-0.5),conf.int=0.95)

#CONTRASTS FOR R TREATMENTS CODING

summary(FM) #GIVES COMPARISON OF DIFFERENCE IN MEANS FROM THE FIRST
#SAME CALCULATION WITH EXPLICIT CONTRASTS
fit.contrast(FM,X,rbind(c(-1,1,0,0),c(-1,0,1,0),c(-1,0,0,1)),conf.int=0.95)

#CONTRASTS FOR COMPARING PAIRS OF MEANS IN 2008 LINEAR MODELS 16
fit.contrast(FM,X,rbind(c(1,1,-1,-1),c(1,-1,1,-1),c(1,-1,-1,1)),conf.int=0.95)