p">=</span> <span class="fl">15</span><span class="op">)</span>,</span></span>
<span class="r-in"><span>    group <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/levels.html" class="external-link">levels</a></span><span class="op">(</span><span class="va">group</span><span class="op">)</span><span class="op">)</span><span class="op">)</span></span></span>
<span class="r-in"><span>    </span></span>
<span class="r-in"><span><span class="va">plot_data</span> <span class="op">&lt;-</