title: knitr how to get exponent/footnotes in latex table using xtable
body: <p>I would like to have a footnote in a cell of a latex table. Usually I would do it with:</p>
  
  <pre><code> ... &amp;   $^{1)}  $ ...     
  </code></pre>
  
  <p>How can I get this using xtable? The following is a minimal example and I tried several ways to get what I want:</p>
  
  <pre><code>\documentclass[9pt]{article}
  
  \begin{document}    
  
  &lt;&lt;echo=TRUE&gt;&gt;=
  df0 &lt;- data.frame(x=c(1:5), y=c('a','b','c','d','e'))
  df0$y &lt;- as.character(df0$y)
  df0$y[df0$y=="a"] &lt;- "$^{1)}$"
  df0$y[df0$y=="b"] &lt;- "$\\^{2)}$"
  df0$y[df0$y=="c"] &lt;- "$^3$"
  df0$y[df0$y=="d"] &lt;- "$\\^4$"
  df0$y[df0$y=="e"] &lt;- "\\$\\^4\\$"
  df0
  @
  
  &lt;&lt;echo=FALSE, results="asis"&gt;&gt;=
  xtable(df0)
  @
  
  \end{document}
  </code></pre>
  
  <p>Any hint appreciated.</p>