ss="op">$</span><span class="va">epoch</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/factor.html" class="external-link">factor</a></span><span class="op">(</span><span class="va">Skulls</span><span class="op">$</span><span class="va">epoch</span>, labels<span class="op">=</span><span class="fu"><a href="https://rdrr.io/r/base/grep.html" class="external-link">sub</a></span><span class="op">(</span><span class="st">"c"</span>,<span class="st">""</span>,<span class="fu">