update.earth: Update an earth model

Description

Update an earth model.

Usage

# S3 method for earth
update(object = stop("no 'object' argument"),
       formula. = NULL, ponly = FALSE, ..., evaluate = TRUE)

Value

The value is the same as that returned by earth. If object is the only parameter then no changes are made --- the returned value will be the same as the original object.

Arguments

object: The earth object
formula.: The formula. argument is treated like earth's formula argument.
ponly: Force pruning only, no forward pass. Default is FALSE, meaning update.earth decides automatically if a forward pass is needed. See note below.
...: Arguments passed on to earth.
evaluate: If TRUE (default) evaluate the new call, else return the call. Mostly for compatibility with the generic update.

Details

If only the following arguments are used, a forward pass is unnecessary, and update.earth will perform only the pruning pass. This is usually much faster for large models.


     object
     glm
     trace
     nprune
     pmethod
     Eval.model.subsets
     Print.pruning.pass
     Force.xtx.prune
     Use.beta.cache
     Endspan.penalty
     Get.leverages

This automatic determination to do a forward pass can be overridden with the ponly argument. If ponly=TRUE the forward pass will be skipped and only the pruning pass will be executed. This is useful for doing a pruning pass with new data. (Use earth's data argument to specify the new data.) Typically in this scenario you would also specify penalty=-1. This is because with sufficient new data, independent of the original training data, the RSS not the GCV should be used for evaluating model subsets (The GCV approximates what the RSS would be on new data --- but here we actually have new data, so why bother approximating. This "use new data for pruning" approach is useful in situations where you don't trust the GCV approximation for your data.) By making penalty=-1, earth will calculate the RSS, not the GCV. See also the description of penalty on the earth help page.

Another (somewhat esoteric) use of ponly=TRUE is to do subset selection with a different penalty from that used to build the original model.

With trace=1, update.earth will tell you if earth's forward pass was skipped.

If you used keepxy=TRUE in your original call to earth, then update.earth will use the saved values of x, y, etc., unless you specify otherwise by arguments to update.earth. It can be helpful to set trace=1 to see which x and y is used by update.earth.

Examples

Run this code

data(ozone1)

(earth.mod <- earth(O3 ~ ., data = ozone1, degree = 2))

update(earth.mod, formula = O3 ~ . - temp) # requires forward pass and pruning

update(earth.mod, nprune = 8)              # requires only pruning

update(earth.mod, penalty=1, ponly=TRUE)   # pruning pass only with a new penalty