title: Binding list of data.tables by columns, and by reference
body: <p>Say I have the following list:</p>
  
  <pre><code>X = list(data.table(1:2,3:4,5:6), 
           data.table(letters[1:2], letters[3:4]))
  </code></pre>
  
  <p>and I would like to bind elements of the list by columns in to a single data.table.
  The output would be the same as produced by</p>
  
  <pre><code>do.call(cbind, X)
  </code></pre>
  
  <p>However, since my original list and containing data tables are quite large, it would be better if I could do this by reference, rather than copying the whole object with <code>cbind()</code>. Is there a way to do it? Something like <code>rbindlist()</code> equivalent for binding by columns, I've seen this marked as to-do...</p>
  
  <p>Apologies if this simple question is already answered somewhere else, and I've missed the answer.</p>