">year</span><span class="op">:</span><span class="va">day</span><span class="op">)</span><span class="op">)</span></span></code></pre></div>
</div>
<div class="section level3">
<h3 id="aggregations">Aggregations<a class="anchor" aria-label="anchor" href="#aggregations"></a>
</h3>
<div class="sourceCode" id="cb23"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="co"># data.table</span></span>
<span><span class="va">flights</span><span class="op">[</span>, <span class="va">.N<