title: R: plot line segment behind points in R
body: <p>I'm using the 'beeswarm' package and want to plot an abline behind my points. The code below will plot the line on top of my points. </p>
  
  <pre><code>library(beeswarm)
  testdf&lt;-data.frame(a=c(1,1,1,2,2,2,3,3,3),b=c(1,2,3,1,4,6,1,3,4))
  beeswarm(b ~ a,data=testdf,col="red",bg="red",pch=21)
  abline(3,0)
  </code></pre>
  
  <p>I know this question has been answered for plots just using base R (such as here: <a href="https://stackoverflow.com/questions/7263743/how-do-i-draw-gridlines-using-abline-that-are-behind-the-data">How do I draw gridlines using abline() that are behind the data?</a>), but these solutions when applied to my data just create two plots one with an abline and one with the beeswarm plot.</p>
  
  <p>Thanks in advance for your help!</p>