t;y&quot;</span></span>
<span id="cb19-5"><a href="#cb19-5" aria-hidden="true"></a></span>
<span id="cb19-6"><a href="#cb19-6" aria-hidden="true"></a><span class="co">## add a new column by reference</span></span>
<span id="cb19-7"><a href="#cb19-7" aria-hidden="true"></a>DT[, z <span class="op">:</span><span class="er">=</span><span class="st"> </span>3L]</span>
<span id="cb19-8"><a href="#cb19-8" aria-hidden="true"></a></span>
<span id="cb19-9"><a href="#cb19-9" aria-hidden="true"></a><span class="co">## 