ss="bs-callout bs-callout-info"></h4>
<ul>
<li><p>We add a new column <code>max_speed</code> using the <code>:=</code> operator by reference.</p></li>
<li><p>We provide the columns to group by the same way as shown in the <em>Introduction to data.table</em> vignette. For each group, <code>max(speed)</code> is computed, which returns a single value. That value is recycled to fit the length of the group. Once again, no copies are being made at all. <code>flights</code> <em>data.table</em> is modified <em>in-p