rpart {rpart}R Documentation

Recursive Partitioning and Regression Trees

Description

Fit a rpart model

Usage

rpart(formula, data, weights, subset, na.action = na.rpart, method,
      model = FALSE, x = FALSE, y = TRUE, parms, control, cost, ...)

Arguments

formula a formula, as in the lm function.
data an optional data frame in which to interpret the variables named in the formula
weights optional case weights.
subset optional expression saying that only a subset of the rows of the data should be used in the fit.
na.action The default action deletes all observations for which y is missing, but keeps those in which one or more predictors are missing.
method one of "anova", "poisson", "class" or "exp". If method is missing then the routine tries to make an intellegent guess. If y is a survival object, then method="exp" is assumed, if y has 2 columns then method="poisson" is assumed, if y is a factor then method="class" is assumed, otherwise method="anova" is assumed. It is wisest to specifiy the method directly, especially as more criteria are added to the function.
Alternatively, method can be a list of functions named init, split and eval.
model if logical: keep a copy of the model frame in the result? If the input value for model is a model frame (likely from an earlier call to the rpart function), then this frame is used rather than constructing new data.
x keep a copy of the x matrix in the result.
y keep a copy of the dependent variable in the result. If missing and model is supplied this defaults to FALSE.
parms optional parameters for the splitting function. Anova splitting has no parameters. Poisson splitting has a single parameter, the coefficient of variation of the prior distribution on the rates. The default value is 1. Exponential splitting has the same parameter as Poisson. For classification splitting, the list can contain any of: the vector of prior probabilities (component prior), the loss matrix (component loss) or the splitting index (component split). The priors must be positive and sum to 1. The loss matrix must have zeros on the diagnoal and positive off-diagonal elements. The splitting index can be gini or information. The default priors are proportional to the data counts, the losses default to 1, and the split defaults to gini.
control options that control details of the rpart algorithm.
cost a vector of non-negative costs, one for each variable in the model. Defaults to one for all variables. These are scalings to be applied when considering splits, so the improvement on splitting on a variable is divided by its cost in deciding which split to choose.
... arguments to rpart.control may also be specified in the call to rpart. They are checked against the list of valid arguments.

Details

This differs from the tree function mainly in its handling of surrogate variables. In most details it follows Breiman et. al. quite closely.

Value

an object of class rpart, a superset of class tree.

References

Breiman, Friedman, Olshen, and Stone. (1984) Classification and Regression Trees. Wadsworth.

See Also

rpart.control, rpart.object, summary.rpart, print.rpart

Examples

fit <- rpart(Kyphosis ~ Age + Number + Start, data=kyphosis)
fit2 <- rpart(Kyphosis ~ Age + Number + Start, data=kyphosis,
              parms=list(prior=c(.65,.35), split='information'))
fit3 <- rpart(Kyphosis ~ Age + Number + Start, data=kyphosis,
              control=rpart.control(cp=.05))
par(mfrow=c(1,2))
plot(fit)
text(fit, use.n=TRUE)
plot(fit2)
text(fit2, use.n=TRUE)

[Package rpart version 3.1-22 Index]