speed <span class="op">:</span><span class="er">=</span><span class="st"> </span>distance <span class="op">/</span><span class="st"> </span>(air_time<span class="op">/</span><span class="dv">60</span>)]     <span class="co">## doesn&#39;t affect &#39;flights&#39;</span></span>
<span id="cb18-4"><a href="#cb18-4" aria-hidden="true"></a>  DT[, .(<span class="dt">max_speed =</span> <span class="kw">max</span>(speed)), by =<span class="st"> </span>month]</span>
<span id="cb18-5"><a href="#cb18-5" aria-hidden="t