>#   planes = n_distinct(tailnum),</span></span>
<span><span class="co">#   flights = n()</span></span>
<span><span class="co"># )</span></span>
<span></span>
<span><span class="fu"><a href="../reference/summarise_dt.html">summarise_dt</a></span><span class="op">(</span><span class="va">flights</span>,planes <span class="op">=</span> <span class="fu"><a href="https://rdatatable.gitlab.io/data.table/reference/duplicated.html" class="external-link">uniqueN</a></span><span class="op">(</span><span class="va">t