By way of simplified example, say you have the following data:
n <- 10
df <- data.frame(x1 = rnorm(n, 3, 1), x2 = rnorm(n, 0, 1))
And you wish to create a model matrix of the following form:
model.matrix(~ df$x1 + df$x2)
or more preferably:
model.matrix(~ x1 + x2, data = df)
but instead by pasting the formula into model.matrix
. I have experimented with the following but encounter errors with all of them:
form1 <- "df$x1 + df$x2"
model.matrix(~ as.formula(form1))
model.matrix(~ eval(parse(text = form1)))
model.matrix(~ paste(form1))
model.matrix(~ form1)
I've also tried the same with the more preferable structure:
form2 <- "x1 + x2, data = df"
Is there a direct solution to this problem? Or is the model.matrix
function not conducive to this approach?
Do you mean something like this?
You need to give
df
as thedata
argument outside ofas.formula
, as thedata
argument defines the environment within which to evaluate the formula.If you don't want to specify the
data
argument you can do