title: from two lists to one by binding elements
body: <p>I have two lists with two elements each,</p>
  
  <pre><code>l1 &lt;- list(data.table(id=1:5, group=1), data.table(id=1:5, group=1))
  l2 &lt;- list(data.table(id=1:5, group=2), data.table(id=1:5, group=2))
  </code></pre>
  
  <p>and I would like to <code>rbind(.)</code> both elements, resulting in a new list with two elements. </p>
  
  <pre><code>&gt; l
  [[1]]
      id group
   1:  1     1
   2:  2     1
   3:  3     1
   4:  4     1
   5:  5     1
   6:  1     2
   7:  2     2
   8:  3     2
   9:  4     2
  10:  5     2
  
  [[2]]
      id group
   1:  1     1
   2:  2     1
   3:  3     1
   4:  4     1
   5:  5     1
   6:  1     2
   7:  2     2
   8:  3     2
   9:  4     2
  10:  5     2
  </code></pre>
  
  <p>However, I only find examples where <code>rbind(.)</code> is applied to bind across elements. I suspect that the solution lies somewhere in <code>lapply(.)</code> but <code>lapply(c(l1,l2),rbind)</code> appears to bind the lists, producing a list of four elements.</p>