title: warning in importing a CSV to R; "-" not meaningful for factors
body: <p>I'm trying to import a set of dates from CSV to R.</p>
  
  <p>Code:</p>
  
  <pre><code>dates &lt;-- read.csv(file="dates.csv",header=FALSE)
  </code></pre>
  
  <p>Result:</p>
  
  <blockquote>
    <p>Warning message:
    In Ops.factor(left) : ‘-’ not meaningful for factors</p>
  </blockquote>
  
  <p>The result is a bunch of NAs.</p>
  
  <p>CSV file when opened in Notepad:</p>
  
  <pre><code>31/07/2014
  30/07/2014
  29/07/2014
  28/07/2014
  25/07/2014
  24/07/2014
  23/07/2014
  22/07/2014
  21/07/2014
  18/07/2014
  17/07/2014
  16/07/2014
  15/07/2014
  14/07/2014
  11/07/2014
  10/07/2014
  9/07/2014
  8/07/2014
  7/07/2014
  4/07/2014
  3/07/2014
  2/07/2014
  1/07/2014
  30/06/2014
  27/06/2014
  26/06/2014
  25/06/2014
  24/06/2014
  23/06/2014
  20/06/2014
  19/06/2014
  18/06/2014
  17/06/2014
  16/06/2014
  13/06/2014
  12/06/2014
  11/06/2014
  10/06/2014
  9/06/2014
  6/06/2014
  </code></pre>