R generate all possible interaction variables

Question

I have a dataframe with variables, say a,b,c,d

dat <- data.frame(a=runif(1e5), b=runif(1e5), c=runif(1e5), d=runif(1e5))

and would like to g

Answer 1

Since model.matrix complains for factors with just one level, you alternatively might want to use stats::terms

labels(terms(~.^2, data = iris[, 1:3]))
# [1] "Sepal.Length"              "Sepal.Width"               "Petal.Length"             
# [4] "Sepal.Length:Sepal.Width"  "Sepal.Length:Petal.Length" "Sepal.Width:Petal.Length"