title: Possibly inconsistent behavior in qplot()?
body: <p>I'm trying to use qplot() to plot a simple time series as one might do using plot().  The x variable is as.POSIXlt and the y is just some continuous measurement.  Here is the code with some brief comments.  Any help on why these data.frames behave differently would be very much appreciated.  As you can see below, I can work around the problem, but I'm curious as to why is doesn't work as I would expect.  </p>
  
  <p>A few details:<br>
  platform: OS X 10.6.4<br>
  R version: R 2.11.0</p>
  
  <p>Disclaimer:  I realize that I could dig into the source code and figure this out myself.  I've never used SO and thought that it might be a nice topic for this forum. </p>
  
  <p>Disclaimer (2):  I'm new to ggplot2</p>
  
  <pre><code>library(ggplot2)
  ws.dat &lt;- read.csv("~/path/to/filename.csv",header=F)
  names(ws.dat) &lt;- c("s","t","w")
  ws.dat$new.t &lt;- as.POSIXlt(ws.dat$t)
  ws.dat[1:5,]
    ##       s                   t    w               new.t
    ## 1 29522 2005-07-02 00:00:00 5.00 2005-07-02 00:00:00
    ## 2 29522 2005-07-02 00:10:00 5.29 2005-07-02 00:10:00
    ## 3 29522 2005-07-02 00:20:00 5.48 2005-07-02 00:20:00
    ## 4 29522 2005-07-02 00:30:00 5.54 2005-07-02 00:30:00
    ## 5 29522 2005-07-02 00:40:00 5.49 2005-07-02 00:40:00
  
  
  ## the following works
  plot(as.POSIXlt(ws.dat$t), ws.dat$w)
  
  ## doesn't work
  qplot(as.POSIXlt(t), w, data = ws.dat)
    ## Error in if (length(range) == 1 || diff(range) == 0) { : 
    ## missing value where TRUE/FALSE needed
  
  ## doesn't work
  ws.dat$new.t &lt;- as.POSIXlt(ws.dat$t)
  qplot(new.t, w, data = ws.dat)
    ## Same error as above
  
  ## Note - I could find a more elegant way of doing this; I'm just trying
  ##   to reproduce as fast as possible.
  new.df &lt;- data.frame(ws.dat$new.t, ws.dat$w)
  new.df[1:5,]
    ##          ws.dat.new.t ws.dat.w
    ## 1 2005-07-02 00:00:00     5.00
    ## 2 2005-07-02 00:10:00     5.29
    ## 3 2005-07-02 00:20:00     5.48
    ## 4 2005-07-02 00:30:00     5.54
    ## 5 2005-07-02 00:40:00     5.49
  
  ## 'works as *I* would expect'; this is != 'works *as* expected' 
  qplot(ws.dat.new.t, ws.dat.w, data = new.df)
  </code></pre>