New PipeOp to create splines expansions.

[nipnipj]

This can be done using splines::ns(). See https://rdrr.io/r/splines/ns.html Maybe there are other alternatives.

[zhjx19]

Looking forward to

[zhjx19]

This can currently be achieved with: pop = po("modelmatrix", formula = ~ splines::ns(x1, 5)) pop$train(list(task))[[1]]$data()