op">)</span>, </span></span>
<span class="r-in"><span>                omittedLevels<span class="op">=</span><span class="cn">FALSE</span>, addAttributes<span class="op">=</span><span class="cn">FALSE</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># Remove NA and omitted Levels</span></span></span>
<span class="r-in"><span><span class="va">om</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/c