get a call object, change parameters and run it again with the new parameters

问题

I have a model generated from a random forest. Inside it, there is a attribute called call, that will give me the what was actually the randomForest called function.

I want to get this parameter, remove one column from the model and run it again.

ex:

library(randomForest)
data(iris)
iris.rf <- randomForest(Species~.-Sepal.Length,  data=iris, prox=TRUE)
iris.rf$call

# want to remove the field Sepal.length as well
# the call should be then 
# randomForest(Species~.-Sepal.Length-Sepal.Width,  data=iris, prox=TRUE)

I have tried converting to a list, pasting the new argument and then adding it again to iris.rf[[2]], but it paste in all parts of the formula.

I cannot get rid of the class call, to change it and then call eval() to run it again.

回答1:

You could use parse on the paste0 object to get a new expression. You could then evaluate that new object as a call.

Maybe something like this:

> iris.rf$call[[2]][3] <- parse(text = with(iris.rf, {
      paste0(call[[2]][3], " - ", rownames(importance)[1])
  }))
> eval(iris.rf$call)
#
# Call:
#  randomForest(formula = Species ~ . - Sepal.Length - Sepal.Width,      
#               data = iris, prox = TRUE) 
#                Type of random forest: classification
#                      Number of trees: 500
# No. of variables tried at each split: 1
#
#         OOB estimate of  error rate: 3.33%
# Confusion matrix:
#            setosa versicolor virginica class.error
# setosa         50          0         0        0.00
# versicolor      0         47         3        0.06
# virginica       0          2        48        0.04

Note that eval(parse(text = ...)) is not something that is recommended, although it does work nicely for this job.

来源：https://stackoverflow.com/questions/25475519/get-a-call-object-change-parameters-and-run-it-again-with-the-new-parameters