title: qplot error: "each group consists of only one observation. Do you need to adjust the group aesthetic?"
body: <p>I am having a problem plotting a line using qplot.  I've reviewed previous posts related to ggplot2 (e.g. <a href="https://stackoverflow.com/questions/16776450/ggplot2-each-group-consists-of-only-one-observation">ggplot2 each group consists of only one observation</a>), but my problem is a bit different.</p>
  
  <p>I only want a simple line graph plotting temperature against time (ymd_hms).  Not two lines.</p>
  
  <p>My data looks like this:</p>
  
  <pre><code>Date.time
  
  2011/06/17 00:00:00
  
  2011/06/17 00:30:00
  
  2011/06/17 01:00:00
  
  2011/06/17 01:30:00
  
  2011/06/17 02:00:00
  
  2011/06/17 02:30:00
  
  2011/06/17 03:00:00
  
  2011/06/17 03:30:00
  
  
  
  
  Temp
  
  71.1
  
  71.1
  
  71.1
  
  71.1
  
  70.8
  
  70.8
  
  70.8
  
  70.5
  </code></pre>
  
  <p>This is the code I've used:</p>
  
  <pre><code>as.POSIXct(data$Date.time, format = "%Y/%m/%d %H:%M:%S") 
  qplot(Date.time, Temp, data=mydata, geom="line")
  But I get this error:
  "Each group consists of only one observation.  Do you need to adjust the group aesthetic?"
  </code></pre>
  
  <p>How can I fix this?  </p>
  
  <p>Thank you!</p>