How to create an empty datatable with columns names and then append datatables to it?
<p>First I want to create an empty datatable with column names but it fails:</p>

<pre><code>data &lt;- data.table(va, vb, vc)

&gt; Error in data.table(va, vb, vc) : object 'va' not found
</code></pre>

<p>Second I want to append datatable to it but it fails too :</p>

<pre><code>data2 &lt;- data.table(va=c(-1,0,1), vb=c(-1,0,1), vc=c(-1,0,1))
data2
   va vb vc
1: -1 -1 -1
2:  0  0  0
3:  1  1  1
merge(data2,data2)

&gt; Error in merge.data.table(data2, data2) : 
      Can not match keys in x and y to automatically determine appropriate `by` parameter. Please set `by` value explicitly.
</code></pre>

<p>Apparently the function can't identify the <code>by</code> parameters with two identical datatables. Any idea?</p>