model.matrix {base} | R Documentation |
model.matrix
creates a design matrix.
model.weights
extracts the weights.
model.matrix (object, ...) model.matrix.lm(object, ...) model.matrix.default(formula, data, contrasts.arg = NULL, xlev = NULL) model.weights(x)
formula |
a model formula or terms object. |
data |
a data frame created with model.frame . |
contrasts.arg |
A list, whose entries are contrasts suitable for
input to the contrasts function and whose names are
the names of columns of data containing factor s. |
xlev |
to be used as argument of model.frame if
data has no "terms" attribute. |
x |
a modle frame. |
The design matrix for a regression model with the specified formula and data.
Chambers and Hastie: "Statistical Models in S".
data(trees) ff <- log(Volume) ~ log(Height) + log(Girth) str(m <- model.frame(ff, trees)) mat <- model.matrix(ff, m) dd <- data.frame(a = gl(3,4), b = gl(4,1,12))# balanced 2-way options("contrasts") model.matrix(~a+b,dd) model.matrix(~a+b,dd,contrasts=list(a="contr.sum")) model.matrix(~a+b,dd,contrasts=list(a="contr.sum",b="contr.poly")) m.orth <- model.matrix(~a+b,dd, contrasts=list(a="contr.helmert")) crossprod(m.orth)# m.orth is ALMOST orthogonal