ata.table by reference</em>, and also combine them with <code>i</code> and <code>by</code>. It is aimed at those who are already familiar with <em>data.table</em> syntax, its general form, how to subset rows in <code>i</code>, select and compute on columns, and perform aggregations by group. If you’re not familiar with these concepts, please read the <em>“Introduction to data.table”</em> vignette first.</p>
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<div id="data" class="section level2">
<h2>Data</h2>
<p>We will use the same <code>fligh