[R] using the design matrix to correctly configure contrasts

[Walmes Zeviani]

Take a look at contrast package. It has functions to handle with user
contrasts. Below you have a reproducible and minimal example using
contrast's functions.

da <- expand.grid(A=factor(paste("A", 1:3, sep="")),
                  B=factor(paste("B", 1:4, sep="")), rep=1:4)
eta <- model.matrix(~A*B, da)%*%matrix(c(0, 1,2, -1,0,1, 0,1,2, 0,0,0))
da$y <- rnorm(da$A, mean=eta, sd=1)

g0 <- lm(y~A*B, data=da)
anova(g0)

require(contrast)

c0 <- contrast(g0,
               list(B="B1", A="A1"),
               list(B="B2", A="A1"))
c0
c0$X

Walmes.

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..(....)... 0ooo...                              Walmes Zeviani
...\..(.....(.....)...     Master in Statistics and Agricultural
Experimentation
....\_)..... )../....       walmeszeviani at hotmail.com, Lavras - MG, Brasil
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