Complexity Parameter of an rpart Model

Extracts, prints and plots the complexity table of an rpart model.

Usage

CP(x, ...)

# S3 method for class 'CP'
print(x, digits = getOption("digits") - 2L, ...)
# S3 method for class 'CP'
plot(x, minline = TRUE, lty = 3, col = 1,
     upper = c("size", "splits", "none"), ...)

Arguments

x: fitted model object of class "rpart". This is assumed to be the result of some function that produces an object with the same named components as that returned by the rpart function.
digits: the number of digits of numbers to print.
minline: whether a horizontal line is drawn 1SE above the minimum of the curve.
lty: line type for this line
col: colour for this line
upper: what is plotted on the top axis: the size of the tree (the number of leaves) ("size"), the number of splits ("splits") or nothing ("none").
...: further arguments passed to print and plot

Details

The complexity parameter table is hidden deep in the entrails of the rpart result object, it is convenient to have a function to extract it.

Value

A list containing the following components:

cp: the complexity table
x: the rpart object

Author

Andri Signorell <andri@signorell.net>

Examples

r.rp <- FitMod(diabetes ~ ., d.pima, fitfn="rpart")

CP(r.rp)
#> 
#> Classification tree:
#> rpart(formula = diabetes ~ ., data = d.pima, model = TRUE, y = TRUE)
#> 
#> Variables actually used in tree construction:
#> [1] age      glucose  insulin  mass     pedigree pregnant pressure
#> 
#> Root node error: 268/768 = 0.34896
#> 
#> n= 768 
#> 
#>         CP nsplit rel error  xerror     xstd
#> 1 0.242537      0   1.00000 1.00000 0.049288
#> 2 0.104478      1   0.75746 0.79851 0.046360
#> 3 0.017413      2   0.65299 0.70149 0.044461
#> 4 0.014925      5   0.60075 0.74627 0.045381
#> 5 0.013060      9   0.54104 0.73881 0.045233
#> 6 0.011194     12   0.49254 0.74627 0.045381
#> 7 0.010000     15   0.45896 0.74627 0.045381
#> 
plot(CP(r.rp))