title: 'x' is a list, but does not have components 'x' and 'y'
body: <p>i am trying to plot a ROC curve for a multiclass problem, using multiclass.roc function from pROC package, but I get this error:</p>
  
  <pre><code>'x' is a list, but does not have components 'x' and 'y'
  </code></pre>
  
  <p>What does this error mean cause searching in the web didn't help me to find an answer. I can print the roc object, but can not plot it.</p>
  
  <p>Thank you!</p>