Creates subsets of a forest. This can be used to subset a number of trees, e.g. from:(from+num), or to remove all null (type="nonnull") trees that were due to errors, or to randomly select a sub forest (type=random).
subforest(forest, num = NULL, type = "nonnull", from = 1)
Brandmaier, A.M., Oertzen, T. v., McArdle, J.J., & Lindenberger, U. (2013). Structural equation model trees. Psychological Methods, 18(1), 71-86.