title: How to remove NA from a factor variable (and from a ggplot chart)?
body: <p>I have a problem with NA in a factor variable since ggplot includes them in the plot as if they are another category/level. I would like to drop the missing data.
  I am sorry I don't have code handy at the moment, I tried to remove factor levels from dataset that I found at <code>data()</code> and it did not work.</p>
  
  <p>Had someone the same problem?</p>
  
  <p>I tried the solution suggested here <a href="https://stackoverflow.com/questions/11403104/remove-unused-factor-levels-from-a-ggplot-bar-plot">Remove unused factor levels from a ggplot bar plot</a> but I get an error</p>
  
  <blockquote>
    <p>Error: unexpected symbol in: mycode</p>
  </blockquote>
  
  <p>Can someone suggest something?</p>
  
  <p>Also, if there is no way to remove them from inside the ggplot code, how can I remove the NA from a factor variable?</p>