title: Error in class == "suv" : comparison (1) is possible only for atomic and list types
body: <p>This is the code i'm trying to run:</p>
  <pre><code>ggplot(data = mpg, mapping = aes (x = displ, y = hwy)) +
    geom_point(mapping = aes(shape = class)) +
    geom_smooth(data = filter(mpg, class == &quot;suv&quot;), se = F)
  </code></pre>
  <p>but get this error:</p>
  <pre><code>Error in class == &quot;suv&quot; : 
    comparison (1) is possible only for atomic and list types
  </code></pre>
  <p>Why is this?</p>