R/getRules.randomForest.R

In katokohaku/featureTweakR: Calculate Actionable Feature Tweaking

#' parse a decision tree in randomForest into list of path as data.frame
#'
#' @param forest  a randomForest object to be parsed
#' @param k       an integer. k-th decision tree in forest will be parsed.
#' @param label.to A character.
#'
#' @return        a list of rules (data.frame), separated by class label of leaf.
#' @examples
#' \dontrun{
#' X <- iris[, 1:(ncol(iris)-1)]
#' true.y <- iris[, ncol(iris)]
#'
#' rf.iris <- randomForest(X, true.y, ntree=30)
#' getRules.randomForest(rf.iris, k=1)
#' getRules.randomForest(rf.iris, k=1, label.to = "virginica")
#' }
#'

getRules.randomForest <- function(forest, k=1, label.to=NULL) {
  stopifnot(class(forest) == "randomForest")
  class.label <- if(is.null(label.to)){
    as.character(forest$classes)
  } else {
    as.character(label.to)
  }
  stopifnot(any(class.label %in% as.character(forest$classes)))

  suppressWarnings(
    tree.df <- randomForest::getTree(rfobj = forest, k=k, labelVar = as.factor(forest$classes))
  )
  colnames(tree.df) <- c("left.daughter", "right.daughter", "split.var",
                         "split.point", "status", "leaf")

  leaf.in.tree.df <- which(tree.df$leaf %in% class.label)
  catf("%i of path will be traced", length(leaf.in.tree.df))

  all.leaf <- pforeach::npforeach(end.of.path = leaf.in.tree.df, .c=list)({
    this.path <- NULL
    this <- end.of.path
    while(TRUE){
      pos.in.left  <- which(tree.df$left.daughter  == this)
      pos.in.right <- which(tree.df$right.daughter == this)

      pos <- pos.in.left
      sym <- "<"
      if(length(pos.in.left) == 0){
        pos <- pos.in.right
        sym <- ">="
      }
      # tree.df[pos, ]
      this.path <- rbind(
        data.frame(node=pos, path.to = this,
                   split.var=tree.df[pos, ]$split.var,
                   lr=sym,
                   point = round(tree.df[pos, ]$split.point, 4),
                   stringsAsFactors = FALSE),
        this.path)
      this <- pos

      if(this == 1){ break() }
    }
    list(leaf = tree.df[end.of.path, ]$leaf, path = this.path)
  })

  path.by.class <- list()
  for(i.label in class.label){
    path.by.class[[i.label]] <-list(leaf = i.label, path = NULL)
  }

  for(i.path in all.leaf){
    path.by.class[[ i.path$leaf ]]$path[[
      length(path.by.class[[ i.path$leaf ]]$path) + 1
      ]] <- i.path$path
  }

  class(path.by.class) <- "decisionTree.rulePath"
  return(path.by.class)
}