dendro_data.rpart function

Extract data from classification tree object for plotting using ggplot.

Extracts data to plot line segments and labels from a rpart::rpart() classification tree object. This data can then be manipulated or plotted, e.g. using ggplot2::ggplot().

## S3 method for class 'rpart'
dendro_data(
  model,
  uniform = FALSE,
  branch = 1,
  compress = FALSE,
  nspace,
  minbranch = 0.3,
  ...
)

Arguments

• model: object of class "tree", e.g. the output of tree()
• uniform: if TRUE, uniform vertical spacing of the nodes is used; this may be less cluttered when fitting a large plot onto a page. The default is to use a non-uniform spacing proportional to the error in the fit.
• branch: controls the shape of the branches from parent to child node. Any number from 0 to 1 is allowed. A value of 1 gives square shouldered branches, a value of 0 give V shaped branches, with other values being intermediate.
• compress: if FALSE, the leaf nodes will be at the horizontal plot coordinates of 1:nleaves. If TRUE, the routine attempts a more compact arrangement of the tree. The compaction algorithm assumes uniform=TRUE; surprisingly, the result is usually an improvement even when that is not the case.
• nspace: the amount of extra space between a node with children and a leaf, as compared to the minimal space between leaves. Applies to compressed trees only. The default is the value of branch.
• minbranch: set the minimum length for a branch to minbranch times the average branch length. This parameter is ignored if uniform=TRUE. Sometimes a split will give very little improvement, or even (in the classification case) no improvement at all. A tree with branch lengths strictly proportional to improvement leaves no room to squeeze in node labels.
• ...: ignored

Returns

A list of three data frames: - segments: a data frame containing the line segment data

• labels: a data frame containing the label text data

• leaf_labels: a data frame containing the leaf label text data

Details

This code is in essence a copy of rpart::plot.rpart(), retaining the plot data but without plotting to a plot device.

Examples

### Demonstrate rpart

if (require(rpart)) {
  require(ggplot2)
  fit <- rpart(Kyphosis ~ Age + Number + Start, method = "class", 
               data = kyphosis)
  fitr <- dendro_data(fit)
  ggplot() +
    geom_segment(data = fitr$segments, 
                 aes(x = x, y = y, xend = xend, yend = yend)
    ) +
    geom_text(data = fitr$labels, aes(x = x, y = y, label = label)) +
    geom_text(data = fitr$leaf_labels, aes(x = x, y = y, label = label)) +
    theme_dendro()
}

See Also

ggdendrogram()

Other dendro_data methods: dendro_data(), dendro_data.tree(), dendrogram_data(), rpart_labels()

Other rpart functions: rpart_labels(), rpart_segments()