pan><span class="op">(</span><span class="st">"a"</span>, <span class="st">"b"</span>, <span class="cn">NA</span><span class="op">)</span>,</span></span>
<span class="r-in"><span>  fct <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/factor.html" class="external-link">as.factor</a></span><span class="op">(</span><span class="fu"><a href="https://rdrr.io/r/base/c.html" class="external-link">c</a></span><span class="op">(</span><span class="st">"a"</span>, <span class="cn">NA</span>,