title: How to define column names in R - ggplot?
body: <p>I'm a R beginner.
  I wrote my script for plotting some data using ggplot.
  This is what I'm talking about, and IS WORKING!:</p>
  
  <pre><code>plotSerie &lt;- ggplot(fileIn, aes(x=DOY_S1, y=S1_VH, fill=variety, group=paste(fileIn$DOY_S1, fileIn$variety, sep="")))+
   geom_boxplot()
  </code></pre>
  
  <p>The problem is that I would like to change the columns to be plotted prior of the ggplot.</p>
  
  <pre><code>  pol &lt;- "VH"
    sensor &lt;- "S1"
    type &lt;- "variety" 
  
    plotSerie &lt;- ggplot(fileIn, aes(x=paste("DOY_",sensor, sep=""), y=paste(sensor,"_", pol, sep=""), fill=type, group= paste(fileIn$paste("DOY_",sensor, sep=""), fileIn$type, sep="")))+
  
    geom_boxplot()
  </code></pre>
  
  <p>But it doesn't work.</p>
  
  <p>Can you help me?</p>
  
  <p>Thank you</p>