>In the two forms of <code>:=</code> shown above, note that we don’t assign the result back to a variable. Because we don’t need to. The input <em>data.table</em> is modified by reference. Let’s go through examples to understand what we mean by this.</p>
<p>For the rest of the vignette, we will work with <code>flights</code> <em>data.table</em>.</p>
<div id="addupdatedelete-columns-by-reference" class="section level2">
<h2>2. Add/update/delete columns <em>by reference</em></h2>
<div id="ref-j" class="