title: SuperLearner Predict error
body: <p>I am using SuperLearner R package.
  I am trying to generate predicted y values for both train and test set.</p>
  
  <p>After fitting a superlearner model without defining a "newX" to get predictions on the train set first so that I can compute MSE and plot predictions vs. actual Y values, I use "predict" command to predict Y values for the test set by running the following code:</p>
  
  <pre><code>sl.cv&lt;-SuperLearner(Y = label, X = train, 
                   SL.library=c("SL.randomForest", "SL.glmnet", "SL.svm"),
                   method = "method.NNLS", verbose=TRUE, cvControl=list(V=10))
  
  pred.sl.cv &lt;- predict(sl.cv, newdata=test, onlySL = T)
  </code></pre>
  
  <p>Then, I get the following error after "predict":
  "Error in object$whichScreen : $ operator is invalid for atomic vectors"</p>
  
  <p>I browsed many online sources to learn how to use "predict" after fitting a SuperLearner model, and I am doing just as what others do: That is, to put the object name of the fitted SuperLearner model (in this case, "sl.cv") followed by the new test set. I didn't even type $ operator. </p>
  
  <p>Why am I getting this error message? How do I solve this problem?</p>
  
  <p>Another question is: Does adding cvControl=list(V=10) as an option make any change? I think the default setting for SuperLearner model is to conduct 10-fold cross-validation. So, removing "cvControl=list(V=10)" will not change anything, right?</p>
  
  <p>I would appreciate your advice. Thank you!</p>