Control for Rpart Fits
Various parameters that control aspects of the
rpart.control(minsplit = 20, minbucket = round(minsplit/3), cp = 0.01, maxcompete = 4, maxsurrogate = 5, usesurrogate = 2, xval = 10, surrogatestyle = 0, maxdepth = 30, ...)
- the minimum number of observations that must exist in a node in order for a split to be attempted.
the minimum number of observations in any terminal
node. If only one of
minsplitis specified, the code either sets
minsplit/3, as appropriate.
complexity parameter. Any split that does not decrease the overall
lack of fit by a factor of
cpis not attempted. For instance, with
anovasplitting, this means that the overall R-squared must increase by
cpat each step. The main role of this parameter is to save computing time by pruning off splits that are obviously not worthwhile. Essentially,the user informs the program that any split which does not improve the fit by
cpwill likely be pruned off by cross-validation, and that hence the program need not pursue it.
- the number of competitor splits retained in the output. It is useful to know not just which split was chosen, but which variable came in second, third, etc.
- the number of surrogate splits retained in the output. If this is set to zero the compute time will be reduced, since approximately half of the computational time (other than setup) is used in the search for surrogate splits.
how to use surrogates in the splitting process.
0means display only; an observation with a missing value for the primary split rule is not sent further down the tree.
1means use surrogates, in order, to split subjects missing the primary variable; if all surrogates are missing the observation is not split. For value
2,if all surrogates are missing, then send the observation in the majority direction. A value of
0corresponds to the action of
2to the recommendations of Breiman et.al (1984).
- number of cross-validations.
controls the selection of a best surrogate.
If set to
0(default) the program uses the total number of correct classification for a potential surrogate variable, if set to
1it uses the percent correct, calculated over the non-missing values of the surrogate. The first option more severely penalizes covariates with a large number of missing values.
Set the maximum depth of any node of the final tree, with the root
node counted as depth 0. Values greater than 30
rpartwill give nonsense results on 32-bit machines.
- mop up other arguments.
A list containing the options.
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