title: Plotting summary statistics
body: <p>For the following data set, </p>
  
  <pre><code>Genre   Amount
  Comedy  10
  Drama   30
  Comedy  20
  Action  20
  Comedy  20
  Drama   20
  </code></pre>
  
  <p>I want to construct a ggplot2 line graph, where the x-axis is <code>Genre</code> and the y-axis is the sum of all amounts (conditional on the <code>Genre</code>).</p>
  
  <p>I have tried the following:</p>
  
  <pre><code>p = ggplot(test, aes(factor(Genre), Gross)) + geom_point()
  p = ggplot(test, aes(factor(Genre), Gross)) + geom_line()
  p = ggplot(test, aes(factor(Genre), sum(Gross))) + geom_line()
  </code></pre>
  
  <p>but to no avail.</p>