><span class="op">[</span><span class="va">carrier</span> <span class="op">==</span> <span class="st">"AA"</span>, </span>
<span>        <span class="fu"><a href="https://rdrr.io/r/base/lapply.html" class="external-link">lapply</a></span><span class="op">(</span><span class="va">.SD</span>, <span class="va">mean</span><span class="op">)</span>, </span>
<span>        by <span class="op">=</span> <span class="fu">.</span><span class="op">(</span><span class="va">origin</span>, <span class="va">dest</span>, <s