title: extract predictor names from varImp
body: <p>I am using the caret package to run a gbm model. Once the model is run, I use the varImp function to extract the list of important predictors (displays top 20). However I would like to capture the names of the predictors in a character list. How do I do that? The object returned from the varImp does not seem to have the attribute that lists the predictor name - only the variable importance. Here is a sample :</p>
  
  <pre><code>gbmModel= train(target ~. , data = trainData, ....other params )
  varimp = varImp(gbmModel, scale=TRUE)
  str(varimp)
  List of 3
   $ importance:'data.frame': 77 obs. of  1 variable:
  ..$ Overall: num [1:77] 6.63 0 5.35 2.01 0 ...
  $ model     : chr "gbm"
  $ calledFrom: chr "varImp"
  - attr(*, "class")= chr "varImp.train"
  ## Display the important variables
  
  varimp
  
  gbm variable importance
  
   only 20 most important variables shown (out of 77)
  
             Overall
  Var126     100.000
  Var189      99.647
  Var113      41.994
  ... And so on
  </code></pre>
  
  <p>I would like a list like ("Var126", "Var189", "Var113" ...)</p>
  
  <p>Thanks in advance,</p>