title: R: why is my ggplot geom_point() symbol not visible?
body: <p>I am trying to place a symbol on the lowest point in a certain time series, which I have plotted with ggplot's geom_line. However, the geom_point is not showing up on the plot. I have myself successfully used geom_point for this kind of thing before by following hadley's example <a href="http://had.co.nz/ggplot2/book/toolbox.r" rel="nofollow">here</a> (search for 'highest &lt;- subset' to get the relevant assignment) so I know very well that it can be done. I'm just at a loss to spot what I have done differently here that is causing it not to display. I'm guessing it's something straightforward like a missing argument or similar - easy points for a pair of fresh eyes, I think.</p>
  
  <p>Minimal example follows:</p>
  
  <pre><code>require(ggplot2)
  fstartdate &lt;- as.Date('2009-06-01')
  
  set.seed(12345)
  x &lt;- data.frame(mydate=seq(as.Date("2003-06-01"), by="month", length.out=103),myval=runif(103, min=180, max=800))
  lowest &lt;- subset(x, myval == min(x[x$mydate &gt;= fstartdate,]$myval))
  
  thisplot &lt;- ggplot() +
      geom_line(data = x, aes(mydate, myval), colour = "blue", size = 0.7) +
      geom_point(data = lowest, size = 5, colour = "red")
  
  print(thisplot)
  </code></pre>