ask as follows:</p>
<div class="sourceCode" id="cb18"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true"></a>foo &lt;-<span class="st"> </span><span class="cf">function</span>(DT) {</span>
<span id="cb18-2"><a href="#cb18-2" aria-hidden="true"></a>  DT &lt;-<span class="st"> </span><span class="kw">copy</span>(DT)                              <span class="co">## deep copy</span></span>
<span id="cb18-3"><a href="#cb18-3" aria-hidden="true"></a>  DT[, 