title: How to solve for importance in R
body: <p>When I typed the command for importance as below importance (<code>model.rf</code>) I get this error:</p>
  
  <blockquote>
    <p>Error in UseMethod("importance") : no applicable method for 'importance' applied to an object of class "c('randomForest.formula', 'randomForest')"</p>
  </blockquote>
  
  <p>How to solve this error?</p>