Change x-axis limits for partykit::lmtree (mob) plots

Question

Just like in title: I'd like to change x-axis limits for partykit::lmtree (mob) plots.

Toy example

Let shape of Y~X+X^2 regression depend on A:

A <- rep(1:5, each=4)
X <- 1:20
Y <- X*A+(A<3)*X^2+rnorm(20, mean=10)

Now build lmtree with polynomial term and plot:

library(partykit)
mytree <- lmtree(Y~poly(X,2,raw=T) | A, minsize=3)
plot(mytree)

To get this:

Limits of X-axis are clearly based on range of poly(X,2,raw=T) not on range of X. How can I change them?

What I have tried

• Use tp_args=list(xlim=c(1,20)). This failed because (I think) there is no xlim parameter in node_bivplot() that controls plots.
• Find some other parameter of node_bivplot() that controls axes. I can't see any.
• Use Y~X+I(X^2) inside lmtree. This produces separate plots for X and I(X^2) on each leaf.

Answer 1

Currently, the xscale and yscale arguments (grid graphics equivalents to the base graphics arguments xlim and ylim) are set internally in node_bivplot() and cannot be modified through arguments.

In your case I would recommend to set up the two regressors from the polynomial manually (X + I(X^2)) and then only create a terminal panel for the first of these two regressors (which = 1):

mytree <- lmtree(Y ~ X + I(X^2) | A, minsize = 3)
plot(mytree, tp_args = list(which = 1))