title: Change default arguments of ROC computation (pROC) in the RFE process (caret) - R
body: <p>I am computing a SVM-RFE model using <code>"ROC"</code> as the metric, with the <code>rfe</code> function (<code>caret</code> package). To my knowledge, the <code>rfe</code> algorithm optimizes the AUC values using the <code>roc</code> function of the <code>pROC</code> package, with its predefined arguments. However, I would like to set the <code>direction</code> argument to <code>"&lt;"</code> instead of <code>"auto"</code> because in some cases the resulting average AUC is computed in reverse (my data is not very good...). This problem is explained in the answer here: <a href="https://stackoverflow.com/questions/37252317/difference-in-average-auc-computation-using-rocr-and-proc-r">Difference in average AUC computation using ROCR and pROC (R)</a></p>
  
  <p>How could I change this default argument value of the <code>roc</code> function in the <code>rfe</code> computation?</p>
  
  <p>I have tried this simple option, but it does not work:</p>
  
  <pre><code>svmRFE_NG3 &lt;- rfe(x = TAll[,2:50],
                 y = TAll[,1],
                 sizes = seq(1,42),
                 metric = "ROC",
                 levels = c("BREAST","LUNG"),
                 direction = "&lt;",
                 rfeControl = FSctrl,
                 ## Options to train()
                 method = "svmLinear",
                 tuneLength = 10,
                 preProc = c("center", "scale"),
                 ## Inner resampling process
                 trControl = TRctrl)
  </code></pre>