title: convert a data.table to a vector rowwise
body: <p>I have a data.table such as:</p>
  
  <pre><code>example &lt;- data.table(fir =c("A", "B", "C", "A","A", "B", "C"), las=c( "B", "C","B", "C", "B", "C","C"))
  
  A   B
  B   C
  C   B
  A   C
  A   B
  B   C
  C   C
  </code></pre>
  
  <p>Though I guess the problem is the same with a data.frame.</p>
  
  <p>and I would like to get a vector as this:</p>
  
  <pre><code>A, B, B, C, C, B, A, C, A, B, B, C, C, C
  </code></pre>
  
  <p>That's, I want to stack every row on the left hand side...</p>
  
  <p>I've tried <strong>unlist(example)</strong> but it extracts the data columnwise instead.</p>
  
  <p>How can I get it?
  I've also tried with apply, transposing and other strange things.</p>