title: What is the difference between geom_line(stat="hline") and geom_hline?
body: <p>I would like to draw a horizontal line <code>yintercept = mean(y)</code> of my data (x, y)</p>
  
  <p><code>geom_line(stat="hline", linetype="dotted", yintercept="mean")</code>  works fine, but </p>
  
  <p><code>geom_hline(linetype="dotted", yintercept="mean")</code> doesn't work for me?</p>
  
  <p>I wonder what are the difference between these 2 functions? I thought <code>geom_hline</code> = <code>geom_line</code> + <code>stat_hline</code>. Is it not?</p>
  
  <h3>Update</h3>
  
  <p>Answered here <a href="https://stackoverflow.com/questions/18786161/is-there-any-difference-between-geom-astat-b-and-stat-bgeom-a">Is there any difference between `geom_a(stat=&quot;b&quot;, ...)` and `stat_b(geom=&quot;a&quot;,...)`?</a></p>
  
  <p><code>geom_hline</code> is just weird!</p>