Get the right hand side variables of an R formula

You want labels and terms; see ?labels, ?terms, and ?terms.object.

labels(terms(f))# [1] "Petal.Length" "Petal.Width" 

In particular, labels.terms returns the "term.labels" attribute of a terms object, which excludes the LHS variable.

If you have a function in your formula, e.g., log, and want to subset the data frame based on the variables, you can use get_all_vars. This will ignore the function and extract the untransformed variables:

f2 <- Species ~ log(Petal.Length) + Petal.Widthget_all_vars(f2[-2], iris)    Petal.Length Petal.Width1            1.4         0.22            1.4         0.23            1.3         0.24            1.5         0.2...

If you just want the variable names, all.vars is a very helpful function:

all.vars(f2[-2])[1] "Petal.Length" "Petal.Width" 

The [-2] is used to exclude the left hand side.

One way is to use subsetting to remove the LHS from the formula. Then you can use model.frame on this:

f[-2]~Petal.Length + Petal.Widthmodel.frame(f[-2],iris)    Petal.Length Petal.Width1            1.4         0.22            1.4         0.23            1.3         0.24            1.5         0.25            1.4         0.26            1.7         0.4...