previous section, except we don’t want to modify <code>flights</code> by reference.</p>
<p>Let’s first delete the <code>speed</code> column we generated in the previous section.</p>
<div class="sourceCode" id="cb17"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true"></a>flights[, speed <span class="op">:</span><span class="er">=</span><span class="st"> </span><span class="ot">NULL</span>]</span></code></pre></div>
<p>Now, we could accomplish the t