title: Using column names with signs of a data frame in a qplot
body: <p>I have a dataset and unfortunately some of the column labels in my <code>dataframe</code> contain signs (- or +). This doesn't seem to bother the <code>dataframe</code>, but when I try to plot this with <code>qplot</code> it throws me an error:</p>
  
  <pre><code>x &lt;- 1:5
  y &lt;- x
  names &lt;- c("1+", "2-")
  
  mydf &lt;- data.frame(x, y)
  colnames(mydf) &lt;- names
  mydf
  qplot(1+, 2-, data = mydf)
  </code></pre>
  
  <p>and if I enclose the column names in quotes it will just give me a category (or something to that effect, it'll give me a plot of "1+" vs. "2-" with one point in the middle).</p>
  
  <p>Is it possible to do this easily? I looked at aes_string but didn't quite understand it (at least not enough to get it to work).</p>
  
  <p>Thanks in advance.</p>
  
  <p>P.S. I have searched for a solution online but can't quite find anything that helps me with this (it could be due to some aspect I don't understand), so I reason it might be because this is a completely retarded naming scheme I have :p.</p>