title: Why does transform fail silently?
body: <p>Say I have a frame with a column of dates: </p>
  
  <pre><code>test.frame$alt_dates &lt;- c('2001-01-04', '2001-05-11', '2001-05-14', '2001-07-24', '2003-12-24', '2004-07-21', '2004-10-15', '2004-12-15', '2005-03-17', '2005-07-18')
  </code></pre>
  
  <p>They start out as characters. Okay:</p>
  
  <pre><code>class(test.frame$alt_dates)
  [1] "character"
  </code></pre>
  
  <p>If I try to use transform to make those dates into dates:</p>
  
  <pre><code>transform(test.frame, alt_dates &lt;- as.Date(alt_dates)
  </code></pre>
  
  <p>R just prints my frame to the console. If I transform the column directly it works fine:</p>
  
  <pre><code>test.frame$alt_dates &lt;- as.Date(test.frame$alt_dates)
  class(test.frame$alt_dates)
  [1] "Date"
  </code></pre>
  
  <p>What am I doing wrong with Transform?</p>
  
  <p>UPDATE: As a few folks noticed, I wasn't assigning the results to anything. So that explains the printing to the screen and the not storing any changes. But it doesn't work even if I do capture the results: </p>
  
  <pre><code>test.frame &lt;- transform(test.frame, more_dates &lt;- as.Date(more_dates))
  class(test.frame$more_dates)
  [1] "character"
  </code></pre>