Better decision tree graphics for rpart via party and partykit

May 29, 2012

(This article was first published on Super Nerdy Cool » R, and kindly contributed to R-bloggers)

I’ve been using Graphviz to create better decision tree graphics “by hand” for rpart objects created in R (final tree). I stumbled on this post that shows how one could convert an rpart object to a party project via the function in partykit to utilize the plot functions in party. It looks quite nice.

I might have to do additional hacking as I like to display the node size and percentage of success in every node. For example, in rpart, I do something like

## rpartObj created from rpart
textRpartCustom <- 
    nclass <- (ncol(yval) - 1L)/2
    group <- yval[, 1L]
    counts <- yval[, 1L + (1L:nclass)]
    if (!is.null(ylevel)) 
        group <- ylevel[group]
    temp1 <- rpart:::formatg(counts, digits)
    if (nclass > 1) {
        ## temp1 <- apply(matrix(temp1, ncol = nclass), 1, paste, 
        ##     collapse = "/")
      temp1 <- matrix(as.numeric(temp1), ncol=nclass)
      ##temp1 <- paste("p=", round(temp1[, 2] / apply(temp1, 1, sum)*100, 1), "%", "; N=", apply(temp1, 1, sum), sep="")
      temp1 <- paste("", round(temp1[, 2] / apply(temp1, 1, sum)*100, 1), "%", "; ", apply(temp1, 1, sum), sep="") 
    if (use.n) {
        out <- paste(format(group, justify = "left"), "\n", temp1, 
            sep = "")
    else {
        out <- format(group, justify = "left")

rpartObj$functions$text <- textRpartCustom

to get these information to display for a classification fit.

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