title: Saving symbols to plot with Trellis
body: <p>I am plotting in xyplot() as per below.  I put symbols on the plot with print(panel.points()) and it works.  But I need to save the plot with the points to a variable (a in the example) so I can use grid arrange to combine it with other plots in the same picture.  Ideas?</p>
  
  <pre><code>dev.off()
  x &lt;- c(1:10)
  y &lt;- c(1:10)
  
  a &lt;- xyplot(y ~ x, type = "l")
  
  trellis.focus("panel", 1, 1, highlight = FALSE) 
  
  print(panel.points(x[c(5,10)], 
                 y[c(5,10)], 
                 pch = 19, 
                 cex = 0.75, 
                 col = c("red", "black")))
  </code></pre>