title: Formatting a character column as numeric with less than and greater than symbols
body: <p>I have a set of data with laboratory submitted calculations of microbiological log reductions.  Sometimes it is only possible to state a value of greater than or less than a certain figure.  Example data here:</p>
  
  <pre><code>test.df &lt;- tribble(
  ~x, ~y, ~z,
  #--|--|----
  "pa", "lab1", "-3.52",
  "pa", "lab2", "&gt;5.0",
  "pa", "lab3", "&lt;-1.567")
  </code></pre>
  
  <p>Are there any routines which would allow me to format this with correct alignment, i.e.,</p>
  
  <pre><code>Organism     Laboratory     LogReduction
  --------     ----------     ------------
  pa           lab1            -3.52
  pa           lab2           &gt; 5.0
  pa           lab3           &lt;-1.567
  </code></pre>
  
  <p>I.e., decimal points line up, and all greater-than or less-than symbols line up as well ?</p>
  
  <p>Basically, I'm trying to end up with a dataframe like this which I can print with kable</p>
  
  <pre><code>test.df &lt;- tribble(
  ~x, ~y, ~z,
  #--|--|----
  "pa", "lab1", " -3.52 ",
  "pa", "lab2", "&gt; 5.0  ",
  "pa", "lab3", "&lt;-1.567")
  </code></pre>
  
  <p>I've tried some sprintf mangling but can't see anything that fits the bill.</p>