| rpart {rpart} | R Documentation |
Fit a rpart model
rpart(formula, data, weights, subset, na.action = na.rpart, method,
model = FALSE, x = FALSE, y = TRUE, parms, control, cost, ...)
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.
|
This differs from the tree function mainly in its handling of surrogate
variables. In most details it follows Breiman et. al. quite closely.
an object of class rpart, a superset of class tree.
Breiman, Friedman, Olshen, and Stone. (1984) Classification and Regression Trees. Wadsworth.
rpart.control, rpart.object,
summary.rpart, print.rpart
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), xpd=NA) # otherwise on some devices the text is clipped
plot(fit)
text(fit, use.n=TRUE)
plot(fit2)
text(fit2, use.n=TRUE)