Hello, All:
What's the simplest way to convert a data.frame into a model.matrix?
One way is given by the following example, modified from the
examples in help(model.matrix):
dd <- data.frame(a = gl(3,4), b = gl(4,1,12))
ab <- model.matrix(~ a + b, dd)
ab0 <- model.matrix(~., dd)
all.equal(ab, ab0)
What do you think about replacing "model.matrix(~ a + b, dd)" in
the current help(model.matrix) with this 3-line expansion?
I suggest this, because I spent a few hours today trying to
convert a data.frame into a model.matrix before finding this.
Also, what do you think about adding something like the following
to the stats package:
model.matrix.data.frame <- function(object, ...){
model.matrix(~., object, ...)
}
And then extend the above example as follows:
ab. <- model.matrix(dd)
all.equal(ab, ab.)
Thanks,
Spencer Graves
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